<table><caption>**Table 7.** Number of contaminants estimated using different published log N − log S relations, in the ULX and HLX samples.</caption><thead><tr><th>Survey</th><th>Moretti+03</th><th>Georgakakis+08</th><th>Kim+07</th><th>Identified</th></tr></thead><tbody><tr><td>2SXPS ULXs</td><td>140<sup>+7</sup><sub>-15</sub></td><td>141<sup>+7</sup><sub>-14</sub></td><td>139<sup>+7</sup><sub>-15</sub></td><td>171</td></tr><tr><td>2SXPS HLXs</td><td>13<sup>+2</sup><sub>-6</sub></td><td>13<sup>+3</sup><sub>-5</sub></td><td>13<sup>+2</sup><sub>-6</sub></td><td>25</td></tr><tr><td>4XMM ULXs</td><td>582<sup>+55</sup><sub>-73</sub></td><td>558<sup>+53</sup><sub>-70</sub></td><td>554<sup>+53</sup><sub>-69</sub></td><td>541</td></tr><tr><td>4XMM HLXs</td><td>136<sup>+34</sup><sub>-44</sub></td><td>137<sup>+33</sup><sub>-44</sub></td><td>135<sup>+33</sup><sub>-43</sub></td><td>121</td></tr><tr><td>CSC2 ULXs</td><td>483<sup>+38</sup><sub>-67</sub></td><td>451<sup>+35</sup><sub>-62</sub></td><td>452<sup>+35</sup><sub>-62</sub></td><td>482</td></tr><tr><td>CSC2 HLXs</td><td>75<sup>+17</sup><sub>-31</sub></td><td>73<sup>+17</sup><sub>-30</sub></td><td>73<sup>+17</sup><sub>-30</sub></td><td>64</td></tr></tbody></table>

**Notes.** Positive and negative errors correspond to the estimates at 10% and 90% of the exclusion radius (3(POSSERR + 0.5)) distribution. The last column gives the number of candidates filtered out by our pipeline as background contaminants, or identified as HLX weak candidates.

contaminants using the 10%, 50% and 90% percentiles of the position error distribution in each sample of candidates. Results are given in Table 7 for the ULX and HLX contaminants, where error bars correspond to the variations in position error. For ULXs, it is comparable to the number of candidates known or classified as AGN, or removed by visual inspection of the optical source. For HLXs, it is similar to the number of background sources (using photometric redshifts) added to the number of HLX candidates flagged as weak. This is a further indication that the selection of ULX and HLX candidates, and thus the automatic classification and the photometric redshifts estimates, are reliable and robust.

Except in the 4XMM sample, our filtering process identifies more ULX candidates as background contaminants than expected from the CXB. Using the CXB curves of Moretti et al. (2003), yielding the larger contamination rates, the 41 remaining background contaminants in our sample thus represent 2.2% of the sample of selected ULXs.

### 4.3. Heterogeneity of the sample and instrumental biases

Because of the different capabilities of *Swift*-XRT, *XMM-Newton* and *Chandra*, we do not expect to probe exactly the same ULX populations in each survey. *Chandra* on-axis observations are more sensitive and have a higher angular resolving power, so it can probe larger distances where the galaxies look smaller. *XMM-Newton* and *Swift* have covered larger sky areas, and the superior follow-up capabilities of *Swift* can also reveal populations of variable ULXs. The design of *Swift* as a gamma-ray burst monitor has led to a more uniform sky coverage, less biased towards galaxies of special interest, so we can expect a lower observer bias of its ULX population. However, the centre-excluding criterion (Eq. (1)) leads to exclude a significant fraction of actual ULXs at low galaxy angular separation. This is particularly the case of *Swift* HLX candidates, which are all offset from their host centre by >10 arcsec, while half of *XMM-Newton* and *Chandra* HLX candidates have lower separations. This probably causes the steeper slope of the 2SXPS XLF above $L_X > 10^{40}$ erg s$^{-1}$.

Another bias in our selection of ULXs and HLXs is the significant difference between *Swift*, *XMM-Newton* and *Chandra* energy bands: in particular, the narrower energy band of the latter probably removes valid candidates just below the ULX luminosity threshold. Assuming a phenomenological absorbed power-law model for ULX spectra, with typical parameters $\Gamma = 2.4$, $n_H = 2 \times 10^{21}$ cm$^{-2}$ (Gladstone et al. 2009), the conversion factor from the *XMM-Newton* 0.2–12 keV band to the *Chandra*

0.5–7 keV band is 0.85, and becomes as low as 0.7 for a photon index $\Gamma \lesssim 2$. If this conversion is valid on average, the *Chandra* XLF break in spiral galaxies would be shifted to up to $\sim 4 \times 10^{39}$ erg s$^{-1}$, better matching the other XLFs.

Nevertheless, results obtained from the XLF and the comparison with XRBs, ULXs and HLXs are comparable between instruments, showing the robustness of both our cleaning pipeline and our statistical study with respect to instrumental biases.

The XLF inferred from 2SXPS, 4XMM and CSC2 are compatible at the 2-σ level except at the faint end $L_X < 5 \times 10^{39}$ erg s$^{-1}$. At these luminosities, most of the sample is made up of sources in galaxies in the distance range of 5–60 Mpc: those sources are most often resolved by *Chandra*, whereas a substantial fraction of *XMM-Newton* and *Swift*-XRT sources are confused (Fig. 1). Moreover, because of the higher noise level and the poorer spatial resolution, sources hidden in diffuse X-ray emission are harder to detect with those facilities. Consequently, the intrinsic slope of the *XMM-Newton* and *Swift* XLF are substantially underestimated at the faint end.

A similar problem occurs at fainter luminosities for *Chandra* sources: as explained in Wang et al. (2016), sources fainter than $10^{38}$ erg s$^{-1}$ are more likely to be below the detection threshold, in particular when located in diffuse emission. This leads to the flattening of the XLF at these luminosities, so that diagnostics on the XLF faint end of XRB must rely on deep observations of close individual galaxies, as done in Mineo et al. (2012) or include a completeness correction as in Wang et al. (2016).

Another moderately significant difference is the steeper slope in the bright end of 2SXPS XLFs, above $\sim 2 \times 10^{40}$ erg s$^{-1}$, while 4XMM and CSC2 are consistent with each other. A closer look at each sample above this luminosity reveals that half of 4XMM and CSC2 candidates are detected in galaxies of apparent diameter $D_{25} < 20$ arcsec, whereas 2SXPS candidates in such galaxies are systematically discarded by the centre exclusion criterion due to their larger position error. There is thus a lack of HLXs in the 2SXPS sample. As a result, the XLF based on *Chandra* sources is probably the most representative of the intrinsic, ‘universal’ XLF of spiral galaxies.

### 4.4. X-ray luminosity function

#### 4.4.1. XLF break

Our work shows significant evidence of the existence of a break between $3 \times 10^{39}$ and $10^{40}$ erg s$^{-1}$. This somewhat agrees with the findings of Swartz et al. (2011) and Mineo et al. (2012), suggesting a cutoff luminosity of $1-2 \times 10^{40}$ erg s$^{-1}$. In contrast, Wang et al. (2016) reported that this break is spuriously caused by the lack of statistics in these studies, and stated that no break is needed at this point of their XLF. We see two reasons for this inconsistency: first, their sample is made up by searching X-ray sources within twice the $D_{25}$ of the galaxy, and they do not implement any procedure to remove the abundant contaminants this implies. These contaminants have an important influence at high luminosities (Fig. 6) and thus can flatten the XLF around $10^{40}$ erg s$^{-1}$. Second, they only considered the differential luminosity function in their XLF fits, showing higher dispersion, so that a break can be buried in this “noise”. In their Fig. 9 showing the cumulative XLF, there might be an hint for a break around $10^{40}$ erg s$^{-1}$.

The precise location of the break varies between samples, with 2SXPS sources yielding the largest value. We argue that the lack of low-luminosity ULXs due to source confusion issues,
<table><caption>**Table 7.** Number of contaminants estimated using different published log N–log S relations, in the ULX and HLX samples.</caption><thead><tr><th>Survey</th><th>Moretti+03</th><th>Georgakakis+08</th><th>Kim+07</th><th>Identified</th></tr></thead><tbody><tr><td>2SXPS ULXs</td><td>140<sup>+7</sup><sub>-15</sub></td><td>141<sup>+7</sup><sub>-14</sub></td><td>139<sup>+7</sup><sub>-15</sub></td><td>171</td></tr><tr><td>2SXPS HLXs</td><td>13<sup>+2</sup><sub>-6</sub></td><td>13<sup>+3</sup><sub>-5</sub></td><td>13<sup>+2</sup><sub>-6</sub></td><td>25</td></tr><tr><td>4XMM ULXs</td><td>582<sup>+55</sup><sub>-73</sub></td><td>558<sup>+53</sup><sub>-70</sub></td><td>554<sup>+53</sup><sub>-69</sub></td><td>541</td></tr><tr><td>4XMM HLXs</td><td>136<sup>+34</sup><sub>-44</sub></td><td>137<sup>+33</sup><sub>-44</sub></td><td>135<sup>+33</sup><sub>-43</sub></td><td>121</td></tr><tr><td>CSC2 ULXs</td><td>483<sup>+38</sup><sub>-67</sub></td><td>451<sup>+35</sup><sub>-62</sub></td><td>452<sup>+35</sup><sub>-62</sub></td><td>482</td></tr><tr><td>CSC2 HLXs</td><td>75<sup>+17</sup><sub>-31</sub></td><td>73<sup>+17</sup><sub>-30</sub></td><td>73<sup>+17</sup><sub>-30</sub></td><td>64</td></tr></tbody></table>

**Notes.** Positive and negative errors correspond to the estimates at 10% and 90% of the exclusion radius (3(POSSERR + 0.5)) distribution. The last column gives the number of candidates filtered out by our pipeline as background contaminants, or identified as HLX weak candidates.

contaminants using the 10%, 50% and 90% percentiles of the position error distribution in each sample of candidates. Results are given in Table 7 for the ULX and HLX contaminants, where error bars correspond to the variations in position error. For ULXs, it is comparable to the number of candidates known or classified as AGN, or removed by visual inspection of the optical source. For HLXs, it is similar to the number of background sources (using photometric redshifts) added to the number of HLX candidates flagged as weak. This is a further indication that the selection of ULX and HLX candidates, and thus the automatic classification and the photometric redshifts estimates, are reliable and robust.

Except in the 4XMM sample, our filtering process identifies more ULX candidates as background contaminants than expected from the CXB. Using the CXB curves of Moretti et al. (2003), yielding the larger contamination rates, the 41 remaining background contaminants in our sample thus represent 2.2% of the sample of selected ULXs.

### 4.3. Heterogeneity of the sample and instrumental biases

Because of the different capabilities of *Swift*-XRT, *XMM-Newton* and *Chandra*, we do not expect to probe exactly the same ULX populations in each survey. *Chandra* on-axis observations are more sensitive and have a higher angular resolving power, so it can probe larger distances where the galaxies look smaller. *XMM-Newton* and *Swift* have covered larger sky areas, and the superior follow-up capabilities of *Swift* can also reveal populations of variable ULXs. The design of *Swift* as a gamma-ray burst monitor has led to a more uniform sky coverage, less biased towards galaxies of special interest, so we can expect a lower observer bias of its ULX population. However, the centre-excluding criterion (Eq. (1)) leads to exclude a significant fraction of actual ULXs at low galaxy angular separation. This is particularly the case of *Swift* HLX candidates, which are all offset from their host centre by >10 arcsec, while half of *XMM-Newton* and *Chandra* HLX candidates have lower separations. This probably causes the steeper slope of the 2SXPS XLF above $L_X > 10^{40}$ erg s$^{-1}$.

Another bias in our selection of ULXs and HLXs is the significant difference between *Swift*, *XMM-Newton* and *Chandra* energy bands: in particular, the narrower energy band of the latter probably removes valid candidates just below the ULX luminosity threshold. Assuming a phenomenological absorbed power-law model for ULX spectra, with typical parameters $\Gamma = 2.4$, $n_H = 2 \times 10^{21}$ cm$^{-2}$ (Gladstone et al. 2009), the conversion factor from the *XMM-Newton* 0.2–12 keV band to the *Chandra*

0.5–7 keV band is 0.85, and becomes as low as 0.7 for a photon index $\Gamma \lesssim 2$. If this conversion is valid on average, the *Chandra* XLF break in spiral galaxies would be shifted to up to $\sim 4 \times 10^{39}$ erg s$^{-1}$, better matching the other XLFs.

Nevertheless, results obtained from the XLF and the comparison with XRBs, ULXs and HLXs are comparable between instruments, showing the robustness of both our cleaning pipeline and our statistical study with respect to instrumental biases.

The XLF inferred from 2SXPS, 4XMM and CSC2 are compatible at the 2-$\sigma$ level except at the faint end $L_X < 5 \times 10^{39}$ erg s$^{-1}$. At these luminosities, most of the sample is made up of sources in galaxies in the distance range of 5–60 Mpc: those sources are most often resolved by *Chandra*, whereas a substantial fraction of *XMM-Newton* and *Swift*-XRT sources are confused (Fig. 1). Moreover, because of the higher noise level and the poorer spatial resolution, sources hidden in diffuse X-ray emission are harder to detect with those facilities. Consequently, the intrinsic slope of the *XMM-Newton* and *Swift* XLF are substantially underestimated at the faint end.

A similar problem occurs at fainter luminosities for *Chandra* sources: as explained in Wang et al. (2016), sources fainter than $10^{38}$ erg s$^{-1}$ are more likely to be below the detection threshold, in particular when located in diffuse emission. This leads to the flattening of the XLF at these luminosities, so that diagnostics on the XLF faint end of XRB must rely on deep observations of close individual galaxies, as done in Mineo et al. (2012) or include a completeness correction as in Wang et al. (2016).

Another moderately significant difference is the steeper slope in the bright end of 2SXPS XLFs, above $\sim 2 \times 10^{40}$ erg s$^{-1}$, while 4XMM and CSC2 are consistent with each other. A closer look at each sample above this luminosity reveals that half of 4XMM and CSC2 candidates are detected in galaxies of apparent diameter $D_{25} < 20$ arcsec, whereas 2SXPS candidates in such galaxies are systematically discarded by the centre exclusion criterion due to their larger position error. There is thus a lack of HLXs in the 2SXPS sample. As a result, the XLF based on *Chandra* sources is probably the most representative of the intrinsic, ‘universal’ XLF of spiral galaxies.

### 4.4. X-ray luminosity function

#### 4.4.1. XLF break

Our work shows significant evidence of the existence of a break between $3 \times 10^{39}$ and $10^{40}$ erg s$^{-1}$. This somewhat agrees with the findings of Swartz et al. (2011) and Mineo et al. (2012), suggesting a cutoff luminosity of $1-2 \times 10^{40}$ erg s$^{-1}$. In contrast, Wang et al. (2016) reported that this break is spuriously caused by the lack of statistics in these studies, and stated that no break is needed at this point of their XLF. We see two reasons for this inconsistency: first, their sample is made up by searching X-ray sources within twice the $D_{25}$ of the galaxy, and they do not implement any procedure to remove the abundant contaminants this implies. These contaminants have an important influence at high luminosities (Fig. 6) and thus can flatten the XLF around $10^{40}$ erg s$^{-1}$. Second, they only considered the differential luminosity function in their XLF fits, showing higher dispersion, so that a break can be buried in this “noise”. In their Fig. 9 showing the cumulative XLF, there might be an hint for a break around $10^{40}$ erg s$^{-1}$.

The precise location of the break varies between samples, with 2SXPS sources yielding the largest value. We argue that the lack of low-luminosity ULXs due to source confusion issues,
given the lower spatial resolution of Swift-XRT, and of HLXs due to the large Swift exclusion radius, are likely to distort the XLF and shift the break towards higher luminosities. This effect was already pointed out by Wang et al. (2016) when considering more distant elliptical galaxies, increasing the population of unresolved sources. Similarly, if ULXs and HLXs have different nature (see Sect. 4.5), adding HLXs in the ULX cumulative XLFs will distort it so that the break will shift towards fainter luminosities and there will be a flattening at the high-luminosity end.

We test how the location of the break is changed when sources >10⁴¹ erg s⁻¹ are removed before fitting the XLF: while it is unchanged for 2SXPS ULXs, the best-fit break luminosity is found increased to (5.7±1.2)×10³⁹ erg s⁻¹ (log(L<sub>break</sub> [erg s⁻¹]) = 39.75) and (9.1 ± 2.6) × 10³⁹ erg s⁻¹ (log(L<sub>break</sub> [erg s⁻¹]) = 39.96) for the CSC2 and 4XMM samples, respectively. The single power-law fit is still excluded. Once converted to the XMM-Newton broad energy band of 0.2–12 keV (assuming an absorbed power-law spectrum with Γ = 1.7, n<sub>H</sub> = 3 × 10²⁰ cm⁻²), the CSC2 break is further moved to ~8×10³⁹ erg s⁻¹ (log(L<sub>break</sub> [erg s⁻¹]) = 39.9), consistent with the break fitted to the 4XMM sample.

More generally, although the use of cumulative XLFs provides higher statistics and may reveal more features, it is also subject to more biases. In particular, the faint end of the cumulative XLF is impacted by all the selection biases, leading to its flattening, while having the smallest poissonian error bars. This is likely to force the faint end of the XLF fit to flatten, potentially shifting the fitted break luminosity towards fainter luminosities to alleviate the tension between the model and the data. When the differential XLF is fitted (in the form dN/d ln L<sub>X</sub> so that the slopes of the cumulative version are conserved), the break is shifted to (6.4±2.4)×10³⁹, (6.5±4.2)×10³⁹, (1.21±0.27)×10⁴⁰ and (7.9 ± 2.5) × 10³⁹ erg s⁻¹ for the samples of CSC2, 4XMM, 2SXPS and all ULXs, respectively. As a result, the break is probably the cutoff feature reported by Mineo et al. (2012) and Swartz et al. (2011) for spiral galaxies. Most recently, this feature was also found in the XLF from deep Chandra observations of the Virgo cluster (Soria et al. 2022), with a normalisation jump occurring in the range 4–5 × 10³⁹ erg s⁻¹.

We investigate the physical reasons for this break. The first possibility is that a different galaxy population is probed in each luminosity bin of the XLF. Indeed, the XLF shape was found to significantly depend on the galaxy properties, with, for example, a flatter slope for more star-forming galaxies (Wang et al. 2016). We find a moderate increase of the mean SFR of ULX hosts in bins of increasing luminosity, with typical values <0.5 M<sub>☉</sub> yr⁻¹ below 5×10³⁹ erg s⁻¹ and >3 M<sub>☉</sub> yr⁻¹ above 10⁴¹ erg s⁻¹. Extrapolating the result of Wang et al. (2016) to higher luminosities, this should produce a flattening of our XLF with luminosity, whereas we find the opposite behaviour. The stellar mass follows the same trend as the SFR, so that each bin probed similar specific SFRs. The XLF break is thus unlikely to be a selection effect of different environments.

Another possibility is that the luminosity break corresponds to the Eddington luminosity of a given class of objects, such as neutron stars or a certain population of black holes. For example, the Eddington luminosity of ~2 M<sub>☉</sub> neutron stars was argued to be consistent with the 5 × 10³⁸ erg s⁻¹ break seen in the luminosity function of LMXB, when accounting for beaming effects and the accretion of helium-rich material (Kim & Fabbiano 2004; Wang et al. 2016). With the same arguments, we could expect the break found in this study to be due to the Eddington luminosity of ~25 M<sub>☉</sub> black holes. Recent modelling works show

that radiative processes allow a luminosity as high as 10⁴⁰ erg s⁻¹ from supercritically accreting 20 M<sub>☉</sub> stellar-mass black holes (Krtička et al. 2022). However, the >50 M<sub>☉</sub> black holes detected by gravitational wave facilities rule out this break to match the maximum mass of stellar-mass black holes, unless the mass distribution of stellar-mass black holes is bimodal (which could be the case if black holes in XRBs and black holes in mergers do not share the same formation channels, Fishbach & Kalogera 2022, but see Belczynski et al. 2021). Moreover, the same luminosity could be reached by the most magnetised neutron stars (Mushtukov et al. 2015), but the discovery of pulsars reaching even greater luminosities (e.g., Israel et al. 2017) may have challenged this interpretation.

On the other hand, the source spectrum, and hardness ratios, may allow better diagnostics of the source nature. Using a sample of 17 ULXs including six PULXs, Gúrpide et al. (2021) find that the secure neutron stars of their sample are among the hardest sources. To probe which type of accretor dominate at different luminosities, and if they all present the same XLF features, we divide our samples in three bins of HR67: soft (HR67 < 0.2), medium (0.2 < HR67 < 0.5) and hard (HR67 > 0.5) ULXs. The result is plotted in Fig. 20, showing no significant difference between each XLF. The possible reason is that HR67 is inefficient to distinguish neutron star and black hole ULXs, or perhaps more interestingly, that a similar break should exist in both populations even if for different physical reasons. For instance, since the contribution of LMXB in spiral galaxies is known to be non-negligible even at ULX luminosities (e.g., Mineo et al. 2012; Lehmer et al. 2019), the break could be the manifestation of a normalisation jump in the XLF due to a luminosity cutoff at a few 10³⁹ erg s⁻¹ for LMXBs, as mentioned in Soria et al. (2022).

Alternatively, the HMXB XLF was found to present a large dispersion in the range 10³⁸–10⁴⁰ erg s⁻¹ related to galaxy metallicity (Lehmer et al. 2021), with a high luminosity cutoff located between 3 × 10³⁹ erg s⁻¹ (low metallicity galaxies, 12 + log(O/H) ≈ 7.6) and 10⁴⁰ erg s⁻¹ (galaxies of solar metallicity, 12 + log(O/H) ≈ 8.7). The metallicity information is absent from GLADE, but we find 106 galaxies in our ULX sample that have a match in HECATE with a metallicity value: 85% of them are in the range 8.4 < 12 + log(O/H) < 8.9, close to solar metallicity, supporting this explanation for the break. In this scenario, the XLF break we obtained may be due to the combination of an excess of luminous HMXB in low metallicity environments followed by a cutoff, and an increasingly large contribution of another type of object at the bright end, possibly intermediate-mass black holes, corresponding to the bulk of HLXs.

### 4.4.2. XLF slopes

Throughout this Section, we compare the best-fit slopes obtained on cumulative XLFs to slope values reported in the literature. Since the latter are often obtained on differential XLF, e.g., dN/dL<sub>X</sub> ∝ L<sub>X</sub><sup>-α</sup> for a simple power-law model, we convert these values to the cumulative case whenever needed (N(> L<sub>X</sub>) ∝ L<sub>X</sub><sup>-α'</sup> where α' = α - 1).

As discussed in the previous section, the fits to the cumulative XLFs are subject to a number of biases which affect the fitted parameters, including the XLF slopes. For example, the inclusion of HLXs flattens the bright end of the distribution. Analysing the cumulative XLF with HLXs removed, we obtain best-fit high-luminosity slopes (α₂) of 1.82 ± 0.1, 1.66 ± 0.13, 1.79 ± 0.14 and 1.80 ± 0.10 for CSC2, 4XMM, 2SXPS and all
given the lower spatial resolution of Swift-XRT, and of HLXs due to the large Swift exclusion radius, are likely to distort the XLF and shift the break towards higher luminosities. This effect was already pointed out by Wang et al. (2016) when considering more distant elliptical galaxies, increasing the population of unresolved sources. Similarly, if ULXs and HLXs have different nature (see Sect. 4.5), adding HLXs in the ULX cumulative XLFs will distort it so that the break will shift towards fainter luminosities and there will be a flattening at the high-luminosity end.

We test how the location of the break is changed when sources >10⁴¹ erg s⁻¹ are removed before fitting the XLF: while it is unchanged for 2SXPS ULXs, the best-fit break luminosity is found increased to (5.7±1.2)×10³⁹ erg s⁻¹ (log(L<sub>break</sub> [erg s⁻¹]) = 39.75) and (9.1 ± 2.6) × 10³⁹ erg s⁻¹ (log(L<sub>break</sub> [erg s⁻¹]) = 39.96) for the CSC2 and 4XMM samples, respectively. The single power-law fit is still excluded. Once converted to the XMM-Newton broad energy band of 0.2–12 keV (assuming an absorbed power-law spectrum with Γ = 1.7, n<sub>H</sub> = 3 × 10²⁰ cm⁻²), the CSC2 break is further moved to ~8×10³⁹ erg s⁻¹ (log(L<sub>break</sub> [erg s⁻¹]) = 39.9), consistent with the break fitted to the 4XMM sample.

More generally, although the use of cumulative XLFs provides higher statistics and may reveal more features, it is also subject to more biases. In particular, the faint end of the cumulative XLF is impacted by all the selection biases, leading to its flattening, while having the smallest poissonian error bars. This is likely to force the faint end of the XLF fit to flatten, potentially shifting the fitted break luminosity towards fainter luminosities to alleviate the tension between the model and the data. When the differential XLF is fitted (in the form dN/d ln L<sub>X</sub> so that the slopes of the cumulative version are conserved), the break is shifted to (6.4±2.4)×10³⁹, (6.5±4.2)×10³⁹, (1.21±0.27)×10⁴⁰ and (7.9 ± 2.5) × 10³⁹ erg s⁻¹ for the samples of CSC2, 4XMM, 2SXPS and all ULXs, respectively. As a result, the break is probably the cutoff feature reported by Mineo et al. (2012) and Swartz et al. (2011) for spiral galaxies. Most recently, this feature was also found in the XLF from deep Chandra observations of the Virgo cluster (Soria et al. 2022), with a normalisation jump occurring in the range 4–5 × 10³⁹ erg s⁻¹.

We investigate the physical reasons for this break. The first possibility is that a different galaxy population is probed in each luminosity bin of the XLF. Indeed, the XLF shape was found to significantly depend on the galaxy properties, with, for example, a flatter slope for more star-forming galaxies (Wang et al. 2016). We find a moderate increase of the mean SFR of ULX hosts in bins of increasing luminosity, with typical values <0.5 M<sub>☉</sub> yr⁻¹ below 5×10³⁹ erg s⁻¹ and >3 M<sub>☉</sub> yr⁻¹ above 10⁴¹ erg s⁻¹. Extrapolating the result of Wang et al. (2016) to higher luminosities, this should produce a flattening of our XLF with luminosity, whereas we find the opposite behaviour. The stellar mass follows the same trend as the SFR, so that each bin probed similar specific SFRs. The XLF break is thus unlikely to be a selection effect of different environments.

Another possibility is that the luminosity break corresponds to the Eddington luminosity of a given class of objects, such as neutron stars or a certain population of black holes. For example, the Eddington luminosity of ~2 M<sub>☉</sub> neutron stars was argued to be consistent with the 5 × 10³⁸ erg s⁻¹ break seen in the luminosity function of LMXB, when accounting for beaming effects and the accretion of helium-rich material (Kim & Fabbiano 2004; Wang et al. 2016). With the same arguments, we could expect the break found in this study to be due to the Eddington luminosity of ~25 M<sub>☉</sub> black holes. Recent modelling works show

that radiative processes allow a luminosity as high as 10⁴⁰ erg s⁻¹ from supercritically accreting 20 M<sub>☉</sub> stellar-mass black holes (Krtička et al. 2022). However, the >50 M<sub>☉</sub> black holes detected by gravitational wave facilities rule out this break to match the maximum mass of stellar-mass black holes, unless the mass distribution of stellar-mass black holes is bimodal (which could be the case if black holes in XRBs and black holes in mergers do not share the same formation channels, Fishbach & Kalogera 2022, but see Belczynski et al. 2021). Moreover, the same luminosity could be reached by the most magnetised neutron stars (Mushtukov et al. 2015), but the discovery of pulsars reaching even greater luminosities (e.g., Israel et al. 2017) may have challenged this interpretation.

On the other hand, the source spectrum, and hardness ratios, may allow better diagnostics of the source nature. Using a sample of 17 ULXs including six PULXs, Gúrpide et al. (2021) find that the secure neutron stars of their sample are among the hardest sources. To probe which type of accretor dominate at different luminosities, and if they all present the same XLF features, we divide our samples in three bins of HR67: soft (HR67 < 0.2), medium (0.2 < HR67 < 0.5) and hard (HR67 > 0.5) ULXs. The result is plotted in Fig. 20, showing no significant difference between each XLF. The possible reason is that HR67 is inefficient to distinguish neutron star and black hole ULXs, or perhaps more interestingly, that a similar break should exist in both populations even if for different physical reasons. For instance, since the contribution of LMXB in spiral galaxies is known to be non-negligible even at ULX luminosities (e.g., Mineo et al. 2012; Lehmer et al. 2019), the break could be the manifestation of a normalisation jump in the XLF due to a luminosity cutoff at a few 10³⁹ erg s⁻¹ for LMXBs, as mentioned in Soria et al. (2022).

Alternatively, the HMXB XLF was found to present a large dispersion in the range 10³⁸–10⁴⁰ erg s⁻¹ related to galaxy metallicity (Lehmer et al. 2021), with a high luminosity cutoff located between 3 × 10³⁹ erg s⁻¹ (low metallicity galaxies, 12 + log(O/H) ≈ 7.6) and 10⁴⁰ erg s⁻¹ (galaxies of solar metallicity, 12 + log(O/H) ≈ 8.7). The metallicity information is absent from GLADE, but we find 106 galaxies in our ULX sample that have a match in HECATE with a metallicity value: 85% of them are in the range 8.4 < 12 + log(O/H) < 8.9, close to solar metallicity, supporting this explanation for the break. In this scenario, the XLF break we obtained may be due to the combination of an excess of luminous HMXB in low metallicity environments followed by a cutoff, and an increasingly large contribution of another type of object at the bright end, possibly intermediate-mass black holes, corresponding to the bulk of HLXs.

### 4.4.2. XLF slopes

Throughout this Section, we compare the best-fit slopes obtained on cumulative XLFs to slope values reported in the literature. Since the latter are often obtained on differential XLF, e.g., dN/dL<sub>X</sub> ∝ L<sub>X</sub><sup>-α</sup> for a simple power-law model, we convert these values to the cumulative case whenever needed (N(> L<sub>X</sub>) ∝ L<sub>X</sub><sup>-α'</sup> where α' = α - 1).

As discussed in the previous section, the fits to the cumulative XLFs are subject to a number of biases which affect the fitted parameters, including the XLF slopes. For example, the inclusion of HLXs flattens the bright end of the distribution. Analysing the cumulative XLF with HLXs removed, we obtain best-fit high-luminosity slopes (α₂) of 1.82 ± 0.1, 1.66 ± 0.13, 1.79 ± 0.14 and 1.80 ± 0.10 for CSC2, 4XMM, 2SXPS and all
<figure><img src="image_22.png" /><figcaption>**Fig. 20.** Deconvolved XLFs of Chandra, XMM-Newton and all selected ULXs in spiral galaxies, after removal of HLX candidates. Three bins of hardness ratio HR67 (see the text for details) are also shown, representing soft (HR67 < 0.2), medium (0.2 < HR67 < 0.5) and hard (HR67 > 0.5) sources.</figcaption></figure>

ULXs, respectively, in better agreement with the values inferred on the ULX-complete galaxies and close to the value 1.73$^{+1.58}_{-0.54}$ obtained by Mineo et al. (2012) for HMXBs in the same luminosity range.

In addition, resolution effects are also likely to distort the XLF, flattening it at the faint end when two low-luminosity ULXs are mistaken for a unique, brighter source. This also explains why the number of ULXs per galaxy decreases between CSC2, 4XMM and 2SXPS samples, with decreasing spatial resolution. Similarly, given the centre exclusion criterion, the larger position errors of Swift lead to the removal of some 'bona fide' HLXs, steepening the high-luminosity slope of the XLF.

Some of these biases can be alleviated by fitting differential XLFs, rather than their cumulative version. The slopes we obtain are indeed different from the cumulative XLF fits, with ($α_1, α_2$) being (0.64±0.16, 1.69±0.17), (0.88±0.27, 1.16±0.12), (0.58±0.11, 1.70±0.18) and (0.82±0.09, 1.38±0.09) for CSC2, 4XMM, 2SXPS and all ULXs, respectively. These low luminosity slope values better agree with the slope of the HMXB XLF in Mineo et al. (2012) and Lehmer et al. (2019), however the high luminosity slopes are not well-constrained.

<figure><img src="image_23.png" /><figcaption>**Fig. 21.** Best-fit slope of the deconvolved cumulative XLF of elliptical galaxies, as a function of the distance limit of the sample.</figcaption></figure>

Unlike spiral galaxies, the XLF we obtained for elliptical galaxies are in disagreement with the steeper ones reported in the literature. For instance, Walton et al. (2011) find a best-fit slope $α = 1.5 ± 0.4$ for their elliptical galaxies, while Wang et al. (2016) obtain steeper slopes $1.80 ± 0.03$, $2.74 ± 0.10$ and $2.29 ± 0.18$ for elliptical, lenticular and all early-type galaxies, respectively. Note that the definition of elliptical galaxies in the present paper includes lenticular galaxies. In nearby galaxies, the XLF of LMXBs is found to present a break at a few $10^{38}$ erg s$^{-1}$ followed by a power-law decrease of slope ~1.8 (Humphrey & Buote 2008; Kim & Fabbiano 2010).

The flatter slope of the XLF for elliptical galaxies in our study is examined. One possibility is that the hot gas content, prominent in these galaxies, is drowning the signal of ULXs well above the limiting luminosity we compute, which does not depend on the background level. In that case the census of ULXs is largely incomplete, up to a higher luminosity. For instance, M 86 has a CSC2 limiting luminosity of $2 × 10^{38}$ erg s$^{-1}$ from Eq. (3) but the only sources detected within the $D_{25}/2$ ellipse have $L_X > 2 × 10^{39}$ erg s$^{-1}$ and $S/N < 3$. At fixed hot gas density, the hot gas flux in a typical aperture increases with galaxy distance, affecting the detection of increasingly bright sources. To test this effect, we fit the deconvolved XLFs for samples with a range of distance limits. Figure 21 shows a clear flattening of the XLF when extending the sample to further distances. Below 70 Mpc, the XLF of 4XMM ULXs becomes flatter than that of CSC2, probably because of the lower spatial resolution of XMM-Newton. Even the closest elliptical galaxies have few low-luminosity ULXs detected by Swift-XRT because of its lower spatial resolution, hence the flat faint end of the XLF and the inconsistent slope. For a distance limit of ~40 Mpc, as adopted in previous studies of this XLF (e.g., Wang et al. 2016), we find a slope in the range 1.6–1.8, in good agreement with values reported in the literature.

Actually, Mineo et al. (2012) noted a large diversity of XLFs from different spiral galaxies. This diversity of XLF is arguably due to different star formation histories, metallicities and initial mass functions. Ongoing efforts to constrain these quantities for a large fraction of galaxies is thus valuable in this regard. The assumption of a universal XLF thus cannot hold regardless of the galaxy environment, and ideally the XLF should be considered in specific bins of (morphology, specific SFR, $M_*$, metallicity), which is beyond the scope of this study.
<figure><img src="image_23.png" /><figcaption>**Fig. 20.** Deconvolved XLFs of Chandra, XMM-Newton and all selected ULXs in spiral galaxies, after removal of HLX candidates. Three bins of hardness ratio HR67 (see the text for details) are also shown, representing soft (HR67 < 0.2), medium (0.2 < HR67 < 0.5) and hard (HR67 > 0.5) sources.</figcaption></figure>

ULXs, respectively, in better agreement with the values inferred on the ULX-complete galaxies and close to the value 1.73$^{+1.58}_{-0.54}$ obtained by Mineo et al. (2012) for HMXBs in the same luminosity range.

In addition, resolution effects are also likely to distort the XLF, flattening it at the faint end when two low-luminosity ULXs are mistaken for a unique, brighter source. This also explains why the number of ULXs per galaxy decreases between CSC2, 4XMM and 2SXPS samples, with decreasing spatial resolution. Similarly, given the centre exclusion criterion, the larger position errors of Swift lead to the removal of some 'bona fide' HLXs, steepening the high-luminosity slope of the XLF.

Some of these biases can be alleviated by fitting differential XLFs, rather than their cumulative version. The slopes we obtain are indeed different from the cumulative XLF fits, with ($α_1, α_2$) being (0.64±0.16, 1.69±0.17), (0.88±0.27, 1.16±0.12), (0.58±0.11, 1.70±0.18) and (0.82±0.09, 1.38±0.09) for CSC2, 4XMM, 2SXPS and all ULXs, respectively. These low luminosity slope values better agree with the slope of the HMXB XLF in Mineo et al. (2012) and Lehmer et al. (2019), however the high luminosity slopes are not well-constrained.

<figure><img src="image_24.png" /><figcaption>**Fig. 21.** Best-fit slope of the deconvolved cumulative XLF of elliptical galaxies, as a function of the distance limit of the sample.</figcaption></figure>

Unlike spiral galaxies, the XLF we obtained for elliptical galaxies are in disagreement with the steeper ones reported in the literature. For instance, Walton et al. (2011) find a best-fit slope $α = 1.5 ± 0.4$ for their elliptical galaxies, while Wang et al. (2016) obtain steeper slopes $1.80 ± 0.03$, $2.74 ± 0.10$ and $2.29 ± 0.18$ for elliptical, lenticular and all early-type galaxies, respectively. Note that the definition of elliptical galaxies in the present paper includes lenticular galaxies. In nearby galaxies, the XLF of LMXBs is found to present a break at a few $10^{38}$ erg s$^{-1}$ followed by a power-law decrease of slope ~1.8 (Humphrey & Buote 2008; Kim & Fabbiano 2010).

The flatter slope of the XLF for elliptical galaxies in our study is examined. One possibility is that the hot gas content, prominent in these galaxies, is drowning the signal of ULXs well above the limiting luminosity we compute, which does not depend on the background level. In that case the census of ULXs is largely incomplete, up to a higher luminosity. For instance, M 86 has a CSC2 limiting luminosity of $2 × 10^{38}$ erg s$^{-1}$ from Eq. (3) but the only sources detected within the $D_{25}/2$ ellipse have $L_X > 2 × 10^{39}$ erg s$^{-1}$ and $S/N < 3$. At fixed hot gas density, the hot gas flux in a typical aperture increases with galaxy distance, affecting the detection of increasingly bright sources. To test this effect, we fit the deconvolved XLFs for samples with a range of distance limits. Figure 21 shows a clear flattening of the XLF when extending the sample to further distances. Below 70 Mpc, the XLF of 4XMM ULXs becomes flatter than that of CSC2, probably because of the lower spatial resolution of XMM-Newton. Even the closest elliptical galaxies have few low-luminosity ULXs detected by Swift-XRT because of its lower spatial resolution, hence the flat faint end of the XLF and the inconsistent slope. For a distance limit of ~40 Mpc, as adopted in previous studies of this XLF (e.g., Wang et al. 2016), we find a slope in the range 1.6–1.8, in good agreement with values reported in the literature.

Actually, Mineo et al. (2012) noted a large diversity of XLFs from different spiral galaxies. This diversity of XLF is arguably due to different star formation histories, metallicities and initial mass functions. Ongoing efforts to constrain these quantities for a large fraction of galaxies is thus valuable in this regard. The assumption of a universal XLF thus cannot hold regardless of the galaxy environment, and ideally the XLF should be considered in specific bins of (morphology, specific SFR, $M_*$, metallicity), which is beyond the scope of this study.
## 4.5. Nature of HLXs

Taking advantage of the large sky coverage and sensitivities of the catalogues we used, we were able to constitute a sample of 191 HLX candidates. Unlike ULXs, their classification by the classifier (mostly as AGN) cannot be used to identify their nature. Their high luminosities and galactocentric distances tend to bias the classifier towards the AGN class, particularly given that no HLX is present in the training sample of the classifier. However, Barrows et al. (2019; hereafter B19) found that their HLX population is at least partly consistent with accreting black holes at the centre of dwarf galaxies, satellites of the matched host. On the other hand, some HLXs are seen to have soft spectra, with most events detected below 1 keV, some of which being explained by the total or partial tidal disruption of a star by an intermediate-mass black hole (Godet et al. 2014; Lin et al. 2018). Their classification as soft sources is therefore expected. The filtering of HLXs thus relies on visual inspection and the removal of known background and foreground sources.

A few contaminants may be left in the sample of selected HLXs. From the $log N - log S$ estimations reported in Table 7, the fraction of contaminants in the 2SXPS, 4XMM and CSC2 samples are ~20%, ~70% and ~60%, after removal of spurious sources and before removal of known background and foreground sources. The shallower sensitivity of 2SXPS results in HLX candidates in nearby galaxies only, hence the lower contamination rate. The high contamination rates obtained for other surveys agree with the 70% estimate of Zolotukhin et al. (2016), but are in contrast with the 7% of contaminants reported in B19. As they explain, this difference is mainly driven by the lower angular sizes of their galaxies, most of them being located beyond 1000 Mpc, a distance range which is not probed by our sample. By using large and deep photometric redshift surveys, we were able to drastically reduce our high initial contamination fraction (background sources represent 85–95% of sources reported in the last column of Table 7). Following the reasoning of Sect. 4.2 on ULX candidates, we conservatively expect the contamination rate among robust candidates (resp. robust and weak candidates) to be ~20% (resp. ~30%). Thus, our slightly larger HLX sample is the result of the larger sky coverage of GLADE, Swift-XRT and XMM-Newton, to provide local analogues to their HLX population, better suited for future individual follow-ups.

We investigate the possible nature of our HLX candidates. First of all, the bimodality of HR67 as shown in Fig. 18 suggests a difference of nature between soft and hard HLXs, the former being rarer and sometimes transient, with at least some of them consistent with partial or full tidal disruption events (e.g., Godet et al. 2014; Lin et al. 2018). No such candidates were present in the sample of B19, rather showing intrinsically hard spectra or important absorption. By construction, some AGN in galaxy pairs are also included in our HLX sample, and flagged as “galaxy pair” candidates. Since such objects are discarded when their true host is in the GLADE sample, the remaining sources represent a minority of our HLX candidates, but their luminosity distribution is consistent with the one of ‘nuclear’ sources (Fig. 7). In contrast, robust HLXs candidates (having no clear optical counterpart and visibly overlapping the area of the galaxy) and weak HLX candidates (having an optical counterpart in Gaia, PanSTARRS, or DES, or visibly offset from the area of the galaxy), taken together or separately, present a steeper luminosity function, consistent with the bright end slope fitted to ULXs. This maybe supports a common mechanism behind the X-ray emission of these objects, such as accreting black holes

<figure><img src="image_24.png" /><figcaption>**Fig. 22.** Radial distribution of all ULXs (filled circles) and robust HLXs (empty squares), showing their surface density as a function of galactocentric distance. Examples of typical galaxy light profiles are shown in solid lines.</figcaption></figure>

of stellar to intermediate mass. However, following the method described in Sect. 3.2 for ULXs, we find a moderately significant difference between the radial distribution of ULXs and HLXs. Figure 22 illustrates this discrepancy: unlike ULXs, HLXs may not follow typical light profiles and may be equally distributed in the extent of their host. This behaviour perhaps supports the scenario in which they are the central accretor of a galaxy satellite or globular cluster.

Unlike ULXs, a significant fraction (~35%) of HLXs is found to have an optical counterpart. The X-ray to optical flux ratio can often give clues on the source nature. For instance, in AGN, the optical-UV emission of the disc scales with the soft X-ray emission, so that their ratio is generally in the range 0.1–10 (e.g., Maccacaro et al. 1988; Barrows et al. 2019; Tranin et al. 2022). Following the methodology of B19, we first convert the B- and R-band fluxes given different matched optical surveys (PanSTARRS, DES, Gaia, SDSS and the Beijing Arizona Sky Survey) to the V-band, using the conversion of Jester et al. (2005). X-ray broad band fluxes are converted to the 0.3–3.5 keV band using the same fixed spectrum as above. While this is surely a limitation of our study, the heterogeneity of our sample and the low signal-to-noise levels do not allow for a more detailed spectral study. For HLXs present in both B19 and this work, we find a mean bias of our CSC2 fluxes of –0.2 dex with respect to their rest-frame unabsorbed fitted fluxes (±0.3 dex deviation), so this estimation is still reasonable for a population analysis. Finally, for X-ray sources having no counterpart, we attempt to compute an upper limit on their optical flux. B19 estimated the local background level directly from optical images, using an annulus of width being twice the radius of the host. However, we argue that such a large area is likely to contain other optical sources and thus bias the sensitivity at the HLX location towards shallower values, as suggested by the bright locus of flux upper limits in their $F_X-F_V$ plane. We adopt a simpler approach in which this sensitivity is assimilated to the flux of the faintest optical source having $S/N > 5$ within a radius of 15 arcsec around the HLX candidate. Flux limits obtained with this method are found to scale well with the limits computed in B19 (±0.5 dex deviation, bias-subtracted), but are on average ten times fainter. Figure 23 shows the $F_X-F_V$ plane resulting from this analysis. In agreement with the finding of B19, most of $F_X/F_V$ values in our sample are consistent with expectations for AGN. The use of more optical surveys allows us to obtain more stringent constraints on the optical flux upper limit.
4.5. Nature of HLXs

Taking advantage of the large sky coverage and sensitivities of the catalogues we used, we were able to constitute a sample of 191 HLX candidates. Unlike ULXs, their classification by the classifier (mostly as AGN) cannot be used to identify their nature. Their high luminosities and galactocentric distances tend to bias the classifier towards the AGN class, particularly given that no HLX is present in the training sample of the classifier. However, Barrows et al. (2019; hereafter B19) found that their HLX population is at least partly consistent with accreting black holes at the centre of dwarf galaxies, satellites of the matched host. On the other hand, some HLXs are seen to have soft spectra, with most events detected below 1 keV, some of which being explained by the total or partial tidal disruption of a star by an intermediate-mass black hole (Godet et al. 2014; Lin et al. 2018). Their classification as soft sources is therefore expected. The filtering of HLXs thus relies on visual inspection and the removal of known background and foreground sources.

A few contaminants may be left in the sample of selected HLXs. From the log N-log S estimations reported in Table 7, the fraction of contaminants in the 2SXPS, 4XMM and CSC2 samples are ~20%, ~70% and ~60%, after removal of spurious sources and before removal of known background and foreground sources. The shallower sensitivity of 2SXPS results in HLX candidates in nearby galaxies only, hence the lower contamination rate. The high contamination rates obtained for other surveys agree with the 70% estimate of Zolotukhin et al. (2016), but are in contrast with the 7% of contaminants reported in B19. As they explain, this difference is mainly driven by the lower angular sizes of their galaxies, most of them being located beyond 1000 Mpc, a distance range which is not probed by our sample. By using large and deep photometric redshift surveys, we were able to drastically reduce our high initial contamination fraction (background sources represent 85–95% of sources reported in the last column of Table 7). Following the reasoning of Sect. 4.2 on ULX candidates, we conservatively expect the contamination rate among robust candidates (resp. robust and weak candidates) to be ~20% (resp. ~30%). Thus, our slightly larger HLX sample is the result of the larger sky coverage of GLADE, Swift-XRT and XMM-Newton, to provide local analogues to their HLX population, better suited for future individual follow-ups.

We investigate the possible nature of our HLX candidates. First of all, the bimodality of HR67 as shown in Fig. 18 suggests a difference of nature between soft and hard HLXs, the former being rarer and sometimes transient, with at least some of them consistent with partial or full tidal disruption events (e.g., Godet et al. 2014; Lin et al. 2018). No such candidates were present in the sample of B19, rather showing intrinsically hard spectra or important absorption. By construction, some AGN in galaxy pairs are also included in our HLX sample, and flagged as “galaxy pair” candidates. Since such objects are discarded when their true host is in the GLADE sample, the remaining sources represent a minority of our HLX candidates, but their luminosity distribution is consistent with the one of ‘nuclear’ sources (Fig. 7). In contrast, robust HLXs candidates (having no clear optical counterpart and visibly overlapping the area of the galaxy) and weak HLX candidates (having an optical counterpart in Gaia, PanSTARRS, or DES, or visibly offset from the area of the galaxy), taken together or separately, present a steeper luminosity function, consistent with the bright end slope fitted to ULXs. This maybe supports a common mechanism behind the X-ray emission of these objects, such as accreting black holes

<figure><img src="image_25.png" /><figcaption>**Fig. 22.** Radial distribution of all ULXs (filled circles) and robust HLXs (empty squares), showing their surface density as a function of galactocentric distance. Examples of typical galaxy light profiles are shown in solid lines.</figcaption></figure>

of stellar to intermediate mass. However, following the method described in Sect. 3.2 for ULXs, we find a moderately significant difference between the radial distribution of ULXs and HLXs. Figure 22 illustrates this discrepancy: unlike ULXs, HLXs may not follow typical light profiles and may be equally distributed in the extent of their host. This behaviour perhaps supports the scenario in which they are the central accretor of a galaxy satellite or globular cluster.

Unlike ULXs, a significant fraction (~35%) of HLXs is found to have an optical counterpart. The X-ray to optical flux ratio can often give clues on the source nature. For instance, in AGN, the optical-UV emission of the disc scales with the soft X-ray emission, so that their ratio is generally in the range 0.1–10 (e.g., Maccacaro et al. 1988; Barrows et al. 2019; Tranin et al. 2022). Following the methodology of B19, we first convert the B- and R-band fluxes given different matched optical surveys (PanSTARRS, DES, Gaia, SDSS and the Beijing Arizona Sky Survey) to the V-band, using the conversion of Jester et al. (2005). X-ray broad band fluxes are converted to the 0.3–3.5 keV band using the same fixed spectrum as above. While this is surely a limitation of our study, the heterogeneity of our sample and the low signal-to-noise levels do not allow for a more detailed spectral study. For HLXs present in both B19 and this work, we find a mean bias of our CSC2 fluxes of –0.2 dex with respect to their rest-frame unabsorbed fitted fluxes (±0.3 dex deviation), so this estimation is still reasonable for a population analysis. Finally, for X-ray sources having no counterpart, we attempt to compute an upper limit on their optical flux. B19 estimated the local background level directly from optical images, using an annulus of width being twice the radius of the host. However, we argue that such a large area is likely to contain other optical sources and thus bias the sensitivity at the HLX location towards shallower values, as suggested by the bright locus of flux upper limits in their $F_X-F_V$ plane. We adopt a simpler approach in which this sensitivity is assimilated to the flux of the faintest optical source having $S/N > 5$ within a radius of 15 arcsec around the HLX candidate. Flux limits obtained with this method are found to scale well with the limits computed in B19 (±0.5 dex deviation, bias-subtracted), but are on average ten times fainter. Figure 23 shows the $F_X-F_V$ plane resulting from this analysis. In agreement with the finding of B19, most of $F_X/F_V$ values in our sample are consistent with expectations for AGN. The use of more optical surveys allows us to obtain more stringent constraints on the optical flux upper limit.
<figure><img src="image_25.png" /><figcaption>**Fig. 23.** $F_X-F_V$ plane of robust and weak HLX candidates, showing their observed 0.3–3.5 keV X-ray flux as a function of the V-band flux of their optical counterpart (filled circles), or the upper limit on $F_V$ at this location (arrows). The grey solid lines indicate ratios of $F_X/F_V = 0.1$, 1 and 10.</figcaption></figure>

Considering the scenario that HLX candidates are indeed accreting black holes associated with their host, we estimate their mass and the mass of their stellar counterpart. Black hole masses are estimated using bolometric corrections of Marconi et al. (2004) and a fixed Eddington ratio. Unlike B19 who compute bolometric luminosities from their unabsorbed hard (2–10 keV) X-ray flux obtained after spectral fitting, we rather use the softer (0.5–2 keV) part of the spectrum which better matches the union of several energy bands in CSC2, 4XMM and 2SXPS, and is less affected by background emission. Since we do not correct for absorption, this approach is likely to yield some underestimated masses, but we estimate this bias to be ≤0.6 dex from a comparison of CSC2 fluxes with B19 fluxes. The derived bolometric corrections are in the range 10–30 depending on the source luminosity (for comparison, the band 2–10 keV would yield corrections in the range 7–20, and B19 use the fixed value 10). Assuming spectral properties similar to their sample, we adopt a value $f_{Edd} = 0.24$ to derive black hole masses, and the standard formula $L_{Edd}[\text{erg s}^{-1}] \approx 1.26 \times 10^{38} M_{BH}[M_{\odot}]$. The resulting masses are in the range $2 \times 10^{3}-2 \times 10^{6} M_{\odot}$ for robust and weak HLXs, with a median value of $4 \times 10^{4} M_{\odot}$. In particular, 122 of these 169 (robust+weak) candidates fall in the IMBH mass range, below $10^{5} M_{\odot}$. Being more luminous, HLXs in galaxy pairs have an estimated black hole mass $\ge 10^{4} M_{\odot}$ with a median at $2 \times 10^{5} M_{\odot}$.

Concerning galaxy stellar masses, as done in B19, we use the mass to light ratio calibrated on optical colours (Bell et al. 2003). Since some optical surveys in our sample do not provide i-band magnitudes, the relation giving $M_{*}/L_{r}$ as a function of the $(g-r)$ colour is used, allowing us to compute $M_{*}$. Point-like optical counterparts of HLXs are assimilated to their stellar associations (we note as a caveat that this neglects the optical contribution from the putative AGN, while on the contrary we previously interpreted $F_V$ as the AGN flux). Another perhaps important bias is that the point source flux $F_r$ is used in this step, instead of the flux integrated over the Sérsic component. Except for galaxy pair candidates, for which $M_{*}$ may well be

<figure><img src="image_26.png" /><figcaption>**Fig. 24.** Black hole mass – stellar mass plane, estimated from the 0.5–2 keV X-ray flux and the $(g-r)$ colour as detailed in the text. Different types of HLX candidates are shown. Upper limits correspond to the stellar mass of the primary host.</figcaption></figure>

largely underestimated, we do not expect this effect to have a large impact on the computed stellar masses. We obtain that most of stellar counterparts of robust and weak HLXs are in the dwarf regime, $M_{*} < 3 \times 10^{9} M_{\odot}$.

The resulting $M_{BH}-M_{*}$ plane is shown in Fig. 24, also showing the scaling relation calibrated by Reines & Volonteri (2015) on local AGN in low-mass galaxies. Upper limits corresponding to the stellar mass of the host are shown for HLXs having no optical counterpart detected in both *g* and *r* bands. While some robust and weak HLXs appear under-massive, most of them are hard sources, with $F_{0.5-2\text{keV}}$ accounting for less than 30% of their broad-band flux: their black hole mass is likely to be underestimated. A second estimation using the extrapolated band 2–10 keV gives black hole masses in the range $2 \times 10^{3}-2 \times 10^{7} M_{\odot}$ for robust and weak HLXs (median $9 \times 10^{4} M_{\odot}$), with these sources all above $3 \times 10^{4} M_{\odot}$. Some galaxy pair candidates are largely under-massive, probably because of an underestimated $M_{BH}$ (occurring for instance if $f_{Edd} < 0.24$, as is generally observed in such massive galaxies). Interestingly, we find a significant proportion (~25%) of overmassive black holes among robust and weak HLXs, supporting a scenario in which these black holes have undergone a merger-free growth and/or that their stellar counterpart have been tidally stripped by the primary host, or is instead a globular cluster.

This contrasts with B19 results who find a broad alignment of their HLXs to the relation of Reines & Volonteri (2015), maybe because our work is focussing on the more local Universe and thus probes lower black hole masses and an earlier growth regime. The proportion of overmassive black hole is further increased if a lower Eddington ratio is applied to compute black hole masses. For example, Baldassare et al. (2017) find a median Eddington ratio of $f_{Edd} = 0.05$ in their sample of active dwarf galaxies, that they obtain through the unabsorbed X-ray luminosity and the black hole mass inferred from the broad Hα line width (e.g., Greene & Ho 2005; Reines et al. 2013). In our study, nevertheless, a more detailed modelling of X-ray spectrum and optical emission, in particular to securely estimate galaxy masses, would be needed to confirm this overmassive locus.

## 5. Summary

Using the three largest X-ray surveys to date, and a galaxy catalogue of unprecedented completeness for the field, we were
<figure><img src="image_26.png" /><figcaption>**Fig. 23.** $F_X-F_V$ plane of robust and weak HLX candidates, showing their observed 0.3–3.5 keV X-ray flux as a function of the V-band flux of their optical counterpart (filled circles), or the upper limit on $F_V$ at this location (arrows). The grey solid lines indicate ratios of $F_X/F_V = 0.1$, 1 and 10.</figcaption></figure>

Considering the scenario that HLX candidates are indeed accreting black holes associated with their host, we estimate their mass and the mass of their stellar counterpart. Black hole masses are estimated using bolometric corrections of Marconi et al. (2004) and a fixed Eddington ratio. Unlike B19 who compute bolometric luminosities from their unabsorbed hard (2–10 keV) X-ray flux obtained after spectral fitting, we rather use the softer (0.5–2 keV) part of the spectrum which better matches the union of several energy bands in CSC2, 4XMM and 2SXPS, and is less affected by background emission. Since we do not correct for absorption, this approach is likely to yield some underestimated masses, but we estimate this bias to be ≤0.6 dex from a comparison of CSC2 fluxes with B19 fluxes. The derived bolometric corrections are in the range 10–30 depending on the source luminosity (for comparison, the band 2–10 keV would yield corrections in the range 7–20, and B19 use the fixed value 10). Assuming spectral properties similar to their sample, we adopt a value $f_{Edd} = 0.24$ to derive black hole masses, and the standard formula $L_{Edd}[\text{erg s}^{-1}] \approx 1.26 \times 10^{38} M_{BH}[M_{\odot}]$. The resulting masses are in the range $2 \times 10^{3}-2 \times 10^{6} M_{\odot}$ for robust and weak HLXs, with a median value of $4 \times 10^{4} M_{\odot}$. In particular, 122 of these 169 (robust+weak) candidates fall in the IMBH mass range, below $10^{5} M_{\odot}$. Being more luminous, HLXs in galaxy pairs have an estimated black hole mass $\ge 10^{4} M_{\odot}$ with a median at $2 \times 10^{5} M_{\odot}$.

Concerning galaxy stellar masses, as done in B19, we use the mass to light ratio calibrated on optical colours (Bell et al. 2003). Since some optical surveys in our sample do not provide i-band magnitudes, the relation giving $M_{*}/L_{r}$ as a function of the $(g-r)$ colour is used, allowing us to compute $M_{*}$. Point-like optical counterparts of HLXs are assimilated to their stellar associations (we note as a caveat that this neglects the optical contribution from the putative AGN, while on the contrary we previously interpreted $F_V$ as the AGN flux). Another perhaps important bias is that the point source flux $F_r$ is used in this step, instead of the flux integrated over the Sérsic component. Except for galaxy pair candidates, for which $M_{*}$ may well be

<figure><img src="image_27.png" /><figcaption>**Fig. 24.** Black hole mass – stellar mass plane, estimated from the 0.5–2 keV X-ray flux and the $(g-r)$ colour as detailed in the text. Different types of HLX candidates are shown. Upper limits correspond to the stellar mass of the primary host.</figcaption></figure>

largely underestimated, we do not expect this effect to have a large impact on the computed stellar masses. We obtain that most of stellar counterparts of robust and weak HLXs are in the dwarf regime, $M_{*} < 3 \times 10^{9} M_{\odot}$.

The resulting $M_{BH}-M_{*}$ plane is shown in Fig. 24, also showing the scaling relation calibrated by Reines & Volonteri (2015) on local AGN in low-mass galaxies. Upper limits corresponding to the stellar mass of the host are shown for HLXs having no optical counterpart detected in both *g* and *r* bands. While some robust and weak HLXs appear under-massive, most of them are hard sources, with $F_{0.5-2\text{keV}}$ accounting for less than 30% of their broad-band flux: their black hole mass is likely to be underestimated. A second estimation using the extrapolated band 2–10 keV gives black hole masses in the range $2 \times 10^{3}-2 \times 10^{7} M_{\odot}$ for robust and weak HLXs (median $9 \times 10^{4} M_{\odot}$), with these sources all above $3 \times 10^{4} M_{\odot}$. Some galaxy pair candidates are largely under-massive, probably because of an underestimated $M_{BH}$ (occurring for instance if $f_{Edd} < 0.24$, as is generally observed in such massive galaxies). Interestingly, we find a significant proportion (~25%) of overmassive black holes among robust and weak HLXs, supporting a scenario in which these black holes have undergone a merger-free growth and/or that their stellar counterpart have been tidally stripped by the primary host, or is instead a globular cluster.

This contrasts with B19 results who find a broad alignment of their HLXs to the relation of Reines & Volonteri (2015), maybe because our work is focussing on the more local Universe and thus probes lower black hole masses and an earlier growth regime. The proportion of overmassive black hole is further increased if a lower Eddington ratio is applied to compute black hole masses. For example, Baldassare et al. (2017) find a median Eddington ratio of $f_{Edd} = 0.05$ in their sample of active dwarf galaxies, that they obtain through the unabsorbed X-ray luminosity and the black hole mass inferred from the broad Hα line width (e.g., Greene & Ho 2005; Reines et al. 2013). In our study, nevertheless, a more detailed modelling of X-ray spectrum and optical emission, in particular to securely estimate galaxy masses, would be needed to confirm this overmassive locus.

## 5. Summary

Using the three largest X-ray surveys to date, and a galaxy catalogue of unprecedented completeness for the field, we were
able to build the largest and cleanest catalogue of ULXs. It
contains 1901 unique sources, built from 304, 667, and 1185
reliable ULXs from 2SXPS, 4XMM, and CSC2, respectively.
They result from a strict filtering pipeline involving off-centre
selection, the removal of all known contaminants, the use of
an automatic, probabilistic classification, and visual inspec-
tion. The contamination rate is estimated to be no greater
than 2%, which is a considerable improvement on recent ULX
catalogues.

We conducted a statistical study of the ULX luminosity func-
tion and preferred environments, and compared them with a
clean XRB sample in terms of hardness and variability. We also
isolated a sample of 191 HLX candidates and investigated their
properties. We report the following results:

1. Thanks to the use of Malmquist-corrected XLFs, consider-
ably enlarging the number of bright sources usable in the
XLF, the presence of a significant break at ~$10^{40}$ erg s$^{-1}$
is confirmed in all three surveys, in contradiction with the
recent claim of Wang et al. (2016).

2. We confirm the trends followed by the ULX rate with the galaxy environment, found in previous studies. The ULX rate is positively correlated with the SFR and stellar mass. While low-luminosity ULXs tend to be hosted more often in spiral galaxies, the occupation fraction of spiral and elliptical galaxies becomes similar at HLX luminosities.

3. No clear hardness or variability difference is seen among the whole populations of ULXs and XRBs. However, from a sample of significantly variable sources, we confirm the opposite evolution of hardness with luminosity between ULXs and XRBs. Half of the sample shows no hardness evolution with luminosity.

4. The 191 HLX candidates include 115 robust HLXs and 54 less certain HLXs. Their optical counterparts and radial distribution, together with the XLF break, suggest a diverse nature as to the X-ray sources at such luminosities. We note that 120 of them are consistent with an accreting IMBH in a dwarf galaxy satellite of the identified host.

In the future, we will study in greater detail the hardness–
luminosity evolution of ULXs and HLXs to better assess their
nature (Amato et al., in prep.), and conduct individual studies of
some HLX outliers. A statistical study of X-ray sources in dwarf
galaxies is also in preparation, to seek IMBHs and wandering
black holes in isolated galaxies and investigate the ULX excess
previously reported in these galaxies.

Acknowledgements. We thank the anonymous referee for his helpful advice and insightful comments that improved the quality of this article. This work benefited from support from the CNES. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement n°101004168, the XMM2ATHENA project. Hugo Tranin acknowledges Xan Astiasarain and Simon Dupourqué for fruitful discussions during the writing of this paper.

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contains 1901 unique sources, built from 304, 667, and 1185
reliable ULXs from 2SXPS, 4XMM, and CSC2, respectively.
They result from a strict filtering pipeline involving off-centre
selection, the removal of all known contaminants, the use of
an automatic, probabilistic classification, and visual inspec-
tion. The contamination rate is estimated to be no greater
than 2%, which is a considerable improvement on recent ULX
catalogues.

We conducted a statistical study of the ULX luminosity func-
tion and preferred environments, and compared them with a
clean XRB sample in terms of hardness and variability. We also
isolated a sample of 191 HLX candidates and investigated their
properties. We report the following results:

1. Thanks to the use of Malmquist-corrected XLFs, consider-
ably enlarging the number of bright sources usable in the
XLF, the presence of a significant break at ~$10^{40}$ erg s$^{-1}$
is confirmed in all three surveys, in contradiction with the
recent claim of Wang et al. (2016).

2. We confirm the trends followed by the ULX rate with the galaxy environment, found in previous studies. The ULX rate is positively correlated with the SFR and stellar mass. While low-luminosity ULXs tend to be hosted more often in spiral galaxies, the occupation fraction of spiral and elliptical galaxies becomes similar at HLX luminosities.

3. No clear hardness or variability difference is seen among the whole populations of ULXs and XRBs. However, from a sample of significantly variable sources, we confirm the opposite evolution of hardness with luminosity between ULXs and XRBs. Half of the sample shows no hardness evolution with luminosity.

4. The 191 HLX candidates include 115 robust HLXs and 54 less certain HLXs. Their optical counterparts and radial distribution, together with the XLF break, suggest a diverse nature as to the X-ray sources at such luminosities. We note that 120 of them are consistent with an accreting IMBH in a dwarf galaxy satellite of the identified host.

In the future, we will study in greater detail the hardness–
luminosity evolution of ULXs and HLXs to better assess their
nature (Amato et al., in prep.), and conduct individual studies of
some HLX outliers. A statistical study of X-ray sources in dwarf
galaxies is also in preparation, to seek IMBHs and wandering
black holes in isolated galaxies and investigate the ULX excess
previously reported in these galaxies.

Acknowledgements. We thank the anonymous referee for his helpful advice and insightful comments that improved the quality of this article. This work benefited from support from the CNES. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement n°101004168, the XMM2ATHENA project. Hugo Tranin acknowledges Xan Astiasarain and Simon Dupourqué for fruitful discussions during the writing of this paper.

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## Appendix A: List of candidates

The following tables present a partial sample of the ULXs and HLXs identified in this study. The full samples are available at the CDS.

<table><caption>**Table A.1.** List of HLX candidates obtained in this study.</caption><thead><tr><th>Name</th><th>RA deg</th><th>Dec deg</th><th>POSERR arcsec</th><th>F<sub>X</sub> erg cm<sup>-2</sup> s<sup>-1</sup></th><th>D Mpc</th><th>Gal. type</th><th>Sep. kpc</th><th>L<sub>X</sub> erg s<sup>-1</sup></th><th>M<sub>BH</sub> M<sub>☉</sub></th><th>M<sub>☉</sub>, Bell M<sub>☉</sub></th><th>Sub-sample</th></tr></thead><tbody><tr><td>2CXO J001143.2-285548</td><td>2.9303</td><td>-28.9301</td><td>1.1</td><td>1.4 &times; 10<sup>-14</sup></td><td>267.9</td><td>E</td><td>11.2</td><td>1.2 &times; 10<sup>41</sup></td><td>2.5 &times; 10<sup>4</sup></td><td>1.8 &times; 10<sup>7</sup></td><td>robust</td></tr><tr><td>2CXO J002234.1+001609</td><td>5.6424</td><td>0.2693</td><td>0.7</td><td>3.7 &times; 10<sup>-15</sup></td><td>485.3</td><td>S0<sup>0</sup></td><td>15.6</td><td>1.0 &times; 10<sup>41</sup></td><td>2.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J005151.7+474019</td><td>12.9658</td><td>47.6720</td><td>0.8</td><td>1.8 &times; 10<sup>-14</sup></td><td>682.5</td><td></td><td>16.7</td><td>10.0 &times; 10<sup>41</sup></td><td>1.9 &times; 10<sup>5</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J010739.2+541226</td><td>16.9134</td><td>54.2074</td><td>0.4</td><td>9.9 &times; 10<sup>-15</sup></td><td>497.8</td><td></td><td>14.3</td><td>2.9 &times; 10<sup>41</sup></td><td>4.1 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J011028.2-460422</td><td>17.6178</td><td>-46.0729</td><td>0.4</td><td>4.9 &times; 10<sup>-13</sup></td><td>90.9</td><td>S0<sup>+</sup></td><td>3.2</td><td>4.9 &times; 10<sup>41</sup></td><td></td><td></td><td>robust</td></tr><tr><td>2CXO J011751.9-265850</td><td>19.4664</td><td>-26.9808</td><td>1.3</td><td>8.5 &times; 10<sup>-15</sup></td><td>463.4</td><td></td><td>20.6</td><td>2.2 &times; 10<sup>41</sup></td><td>7.1 &times; 10<sup>4</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J011854.9-010551</td><td>19.7288</td><td>-1.0976</td><td>0.5</td><td>2.0 &times; 10<sup>-14</sup></td><td>557.2</td><td>E</td><td>13.4</td><td>7.5 &times; 10<sup>41</sup></td><td>1.2 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J023659.5-511548</td><td>39.2481</td><td>-51.2636</td><td>2.8</td><td>4.7 &times; 10<sup>-14</sup></td><td>343.6</td><td></td><td>24.6</td><td>6.6 &times; 10<sup>41</sup></td><td>1.1 &times; 10<sup>5</sup></td><td>5.8 &times; 10<sup>7</sup></td><td>robust</td></tr><tr><td>2CXO J024106.1-081711</td><td>40.2757</td><td>-8.2865</td><td>0.6</td><td>3.3 &times; 10<sup>-15</sup></td><td>636.8</td><td></td><td>24.6</td><td>1.6 &times; 10<sup>41</sup></td><td>2.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J024228.5-000202</td><td>40.6188</td><td>-0.0340</td><td>0.4</td><td>7.1 &times; 10<sup>-15</sup></td><td>691.8</td><td>E</td><td>27.3</td><td>4.1 &times; 10<sup>41</sup></td><td>8.8 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J025843.0-523930</td><td>44.6794</td><td>-52.6584</td><td>0.5</td><td>4.7 &times; 10<sup>-15</sup></td><td>428.3</td><td></td><td>9.5</td><td>1.0 &times; 10<sup>41</sup></td><td></td><td></td><td>robust</td></tr><tr><td>2CXO J025921.5+132913</td><td>44.8398</td><td>13.4871</td><td>0.6</td><td>8.0 &times; 10<sup>-15</sup></td><td>487.5</td><td></td><td>8.2</td><td>2.3 &times; 10<sup>41</sup></td><td>3.0 &times; 10<sup>4</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J031049.4-265431</td><td>47.7062</td><td>-26.9088</td><td>0.8</td><td>2.0 &times; 10<sup>-14</sup></td><td>597.0</td><td></td><td>14.8</td><td>8.6 &times; 10<sup>41</sup></td><td>1.6 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J034115.1+152335</td><td>55.3129</td><td>15.3932</td><td>0.4</td><td>2.7 &times; 10<sup>-14</sup></td><td>184.4</td><td></td><td>3.8</td><td>1.1 &times; 10<sup>41</sup></td><td>1.5 &times; 10<sup>4</sup></td><td>3.5 &times; 10<sup>7</sup></td><td>weak</td></tr><tr><td>2CXO J034231.8-533841</td><td>55.6325</td><td>-53.6449</td><td>0.4</td><td>2.3 &times; 10<sup>-14</sup></td><td>270.4</td><td>E</td><td>12.2</td><td>2.0 &times; 10<sup>41</sup></td><td>3.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J041338.6+102803</td><td>63.4112</td><td>10.4678</td><td>0.5</td><td>6.0 &times; 10<sup>-15</sup></td><td>405.5</td><td></td><td>10.7</td><td>1.2 &times; 10<sup>41</sup></td><td>1.7 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J043338.4-131612</td><td>68.4101</td><td>-13.2702</td><td>0.4</td><td>5.2 &times; 10<sup>-14</sup></td><td>141.9</td><td>S0<sup>-</sup></td><td>19.8</td><td>1.2 &times; 10<sup>41</sup></td><td>2.0 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J044921.6-485545</td><td>72.3403</td><td>-48.9294</td><td>0.9</td><td>6.7 &times; 10<sup>-15</sup></td><td>355.9</td><td></td><td>6.7</td><td>1.0 &times; 10<sup>41</sup></td><td>1.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J055107.0-570640</td><td>87.7793</td><td>-57.1111</td><td>0.5</td><td>1.5 &times; 10<sup>-14</sup></td><td>267.9</td><td></td><td>15.3</td><td>1.3 &times; 10<sup>41</sup></td><td>2.9 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J061620.8-215616</td><td>94.0867</td><td>-21.9379</td><td>0.5</td><td>1.8 &times; 10<sup>-14</sup></td><td>1.0 &times; 10<sup>3</sup></td><td></td><td>13.2</td><td>2.3 &times; 10<sup>42</sup></td><td>2.1 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J062648.6-543208</td><td>96.7028</td><td>-54.5357</td><td>0.5</td><td>7.5 &times; 10<sup>-14</sup></td><td>225.9</td><td>E</td><td>27.9</td><td>4.6 &times; 10<sup>41</sup></td><td>4.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J071051.5-561009</td><td>107.7150</td><td>-56.1694</td><td>0.8</td><td>1.9 &times; 10<sup>-14</sup></td><td>562.3</td><td></td><td>14.3</td><td>7.2 &times; 10<sup>41</sup></td><td>1.3 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J071644.9+372828</td><td>109.1875</td><td>37.4746</td><td>1.3</td><td>2.5 &times; 10<sup>-14</sup></td><td>317.9</td><td></td><td>14.0</td><td>3.0 &times; 10<sup>41</sup></td><td>4.0 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J074735.8+554113</td><td>116.8994</td><td>55.6870</td><td>0.5</td><td>4.0 &times; 10<sup>-14</sup></td><td>152.1</td><td></td><td>4.2</td><td>1.1 &times; 10<sup>41</sup></td><td>1.6 &times; 10<sup>4</sup></td><td>2.5 &times; 10<sup>9</sup></td><td>weak</td></tr><tr><td>2CXO J081654.4-073931</td><td>124.2271</td><td>-7.6588</td><td>1.4</td><td>1.3 &times; 10<sup>-14</sup></td><td>311.2</td><td></td><td>13.7</td><td>1.5 &times; 10<sup>41</sup></td><td>2.8 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J082213.9+210535</td><td>125.5665</td><td>21.0933</td><td>0.5</td><td>1.2 &times; 10<sup>-13</sup></td><td>92.3</td><td>S0<sup>-</sup></td><td>1.9</td><td>1.2 &times; 10<sup>41</sup></td><td>2.2 &times; 10<sup>4</sup></td><td>3.0 &times; 10<sup>10</sup></td><td>robust</td></tr><tr><td>2CXO J084128.8+322447</td><td>130.3700</td><td>32.4133</td><td>0.4</td><td>1.2 &times; 10<sup>-14</sup></td><td>295.1</td><td>S0<sup>0</sup></td><td>11.4</td><td>1.3 &times; 10<sup>41</sup></td><td>2.4 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J084135.0+010156</td><td>130.3962</td><td>1.0323</td><td>0.4</td><td>6.6 &times; 10<sup>-14</sup></td><td>503.5</td><td></td><td>7.0</td><td>2.0 &times; 10<sup>42</sup></td><td>3.8 &times; 10<sup>5</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J091449.0+085321</td><td>138.7045</td><td>8.8892</td><td>0.4</td><td>6.8 &times; 10<sup>-13</sup></td><td>648.6</td><td>E</td><td>7.9</td><td>3.4 &times; 10<sup>43</sup></td><td>1.7 &times; 10<sup>7</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J101239.8-010628</td><td>153.1662</td><td>-1.1078</td><td>0.5</td><td>9.5 &times; 10<sup>-15</sup></td><td>438.5</td><td>Sa</td><td>9.4</td><td>2.2 &times; 10<sup>41</sup></td><td>4.1 &times; 10<sup>4</sup></td><td>2.6 &times; 10<sup>4</sup></td><td>galaxy pair</td></tr><tr><td>2CXO J103619.8-273939</td><td>159.0827</td><td>-27.6610</td><td>0.9</td><td>8.6 &times; 10<sup>-15</sup></td><td>430.5</td><td>S0<sup>+</sup></td><td>27.1</td><td>1.9 &times; 10<sup>41</sup></td><td>2.9 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J103844.2+485220</td><td>159.6845</td><td>48.8724</td><td>0.4</td><td>9.2 &times; 10<sup>-15</sup></td><td>539.5</td><td></td><td>13.9</td><td>3.2 &times; 10<sup>41</sup></td><td>5.4 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J104142.2+400035</td><td>160.4262</td><td>40.0098</td><td>0.9</td><td>1.5 &times; 10<sup>-14</sup></td><td>642.7</td><td></td><td>24.7</td><td>7.6 &times; 10<sup>41</sup></td><td></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J105210.4+552243</td><td>163.0435</td><td>55.3786</td><td>0.5</td><td>6.9 &times; 10<sup>-15</sup></td><td>669.9</td><td>Sb</td><td>12.2</td><td>3.7 &times; 10<sup>41</sup></td><td>5.7 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J111610.0+013035</td><td>169.0418</td><td>1.5098</td><td>0.5</td><td>1.7 &times; 10<sup>-14</sup></td><td>500.9</td><td>Sbc</td><td>11.9</td><td>5.2 &times; 10<sup>41</sup></td><td>1.1 &times; 10<sup>5</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J112002.6+132830</td><td>170.0112</td><td>13.4752</td><td>2.0</td><td>4.2 &times; 10<sup>-15</sup></td><td>586.1</td><td>Sc</td><td>20.6</td><td>1.7 &times; 10<sup>41</sup></td><td>2.2 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J112110.9-232331</td><td>170.2958</td><td>23.3922</td><td>0.6</td><td>4.2 &times; 10<sup>-15</sup></td><td>513.2</td><td>E</td><td>13.1</td><td>1.3 &times; 10<sup>41</sup></td><td>2.5 &times; 10<sup>4</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J112255.5+010601</td><td>170.7313</td><td>1.1004</td><td>0.4</td><td>2.4 &times; 10<sup>-14</sup></td><td>342.0</td><td>E</td><td>17.5</td><td>3.4 &times; 10<sup>41</sup></td><td>8.1 &times; 10<sup>4</sup></td><td>3.3 &times; 10<sup>8</sup></td><td>weak</td></tr><tr><td>2CXO J121756.3+280941</td><td>184.4849</td><td>28.1615</td><td>0.5</td><td>1.2 &times; 10<sup>-14</sup></td><td>613.8</td><td>E</td><td>17.1</td><td>5.3 &times; 10<sup>41</sup></td><td>1.1 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J122155.1+271022</td><td>185.4796</td><td>27.1728</td><td>0.4</td><td>1.2 &times; 10<sup>-14</sup></td><td>363.1</td><td>E</td><td>6.4</td><td>1.9 &times; 10<sup>41</sup></td><td>2.0 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J123307.6+091942</td><td>188.2820</td><td>9.3285</td><td>0.6</td><td>3.3 &times; 10<sup>-14</sup></td><td>309.0</td><td>Sd</td><td>6.1</td><td>3.7 &times; 10<sup>41</sup></td><td>8.0 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J123605.6+163213</td><td>189.0235</td><td>16.5370</td><td>1.4</td><td>9.7 &times; 10<sup>-15</sup></td><td>318.0</td><td>E</td><td>12.5</td><td>1.2 &times; 10<sup>41</sup></td><td>1.3 &times; 10<sup>4</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J124208.4+331854</td><td>190.5351</td><td>33.3151</td><td>0.4</td><td>8.9 &times; 10<sup>-14</sup></td><td>701.9</td><td>E</td><td>15.2</td><td>5.3 &times; 10<sup>42</sup></td><td>1.3 &times; 10<sup>6</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J130155.9+291815</td><td>195.4833</td><td>29.3044</td><td>1.2</td><td>1.8 &times; 10<sup>-14</sup></td><td>776.2</td><td></td><td>30.3</td><td>1.3 &times; 10<sup>42</sup></td><td></td><td></td><td>robust</td></tr><tr><td>2CXO J131133.3-011656</td><td>197.8891</td><td>-1.2824</td><td>0.4</td><td>6.6 &times; 10<sup>-15</sup></td><td>895.4</td><td></td><td>22.3</td><td>6.3 &times; 10<sup>41</sup></td><td>1.2 &times; 10<sup>5</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J131619.4+620610</td><td>199.0809</td><td>62.1029</td><td>0.9</td><td>1.4 &times; 10<sup>-14</sup></td><td>610.9</td><td>E</td><td>14.4</td><td>6.1 &times; 10<sup>41</sup></td><td>9.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J132519.7-313607</td><td>201.3324</td><td>-31.6021</td><td>0.4</td><td>5.5 &times; 10<sup>-14</sup></td><td>214.8</td><td></td><td>4.0</td><td>3.0 &times; 10<sup>41</sup></td><td>8.1 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J133338.8-314045</td><td>203.4120</td><td>-31.6792</td><td>0.5</td><td>2.3 &times; 10<sup>-14</sup></td><td>214.8</td><td>S0<sup>+</sup></td><td>55.0</td><td>1.3 &times; 10<sup>41</sup></td><td>2.2 &times; 10<sup>3</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J134736.4+173404</td><td>206.9018</td><td>17.5680</td><td>0.4</td><td>3.2 &times; 10<sup>-13</sup></td><td>199.2</td><td>Sbc</td><td>8.2</td><td>1.5 &times; 10<sup>42</sup></td><td>4.5 &times; 10<sup>5</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J140155.7-113809</td><td>210.4823</td><td>-11.6360</td><td>0.4</td><td>3.2 &times; 10<sup>-14</sup></td><td>230.3</td><td></td><td>5.4</td><td>2.0 &times; 10<sup>41</sup></td><td>3.1 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J142010.7+533348</td><td>215.0448</td><td>53.5635</td><td>0.6</td><td>1.2 &times; 10<sup>-14</sup></td><td>293.8</td><td>Irr</td><td>8.3</td><td>1.2 &times; 10<sup>41</sup></td><td>1.6 &times; 10<sup>4</sup></td><td>2.1 &times; 10<sup>6</sup></td><td>robust</td></tr><tr><td>2CXO J145409.9+183700</td><td>223.5415</td><td>18.6169</td><td>1.6</td><td>4.0 &times; 10<sup>-15</sup></td><td>520.0</td><td>Sc</td><td>24.2</td><td>1.3 &times; 10<sup>41</sup></td><td>2.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J150930.4+333330</td><td>227.3769</td><td>33.5585</td><td>0.6</td><td>3.1 &times; 10<sup>-14</sup></td><td>1.0 &times; 10<sup>3</sup></td><td></td><td>24.3</td><td>4.0 &times; 10<sup>42</sup></td><td>9.3 &times; 10<sup>5</sup></td><td>5.5 &times; 10<sup>9</sup></td><td>weak</td></tr><tr><td>2CXO J150940.1+333033</td><td>227.4172</td><td>33.5094</td><td>0.6</td><td>7.6 &times; 10<sup>-15</sup></td><td>549.5</td><td>E</td><td>13.4</td><td>2.8 &times; 10<sup>41</sup></td><td>6.9 &times; 10<sup>4</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J152435.6+295302</td><td>231.1486</td><td>29.8841</td><td>0.7</td><td>3.2 &times; 10<sup>-15</sup></td><td>557.2</td><td></td><td>14.7</td><td>1.2 &times; 10<sup>41</sup></td><td>4.5 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J153143.2+240421</td><td>232.9304</td><td>24.0725</td><td>0.4</td><td>5.7 &times; 10<sup>-14</sup></td><td>438.5</td><td>Sab</td><td>5.9</td><td>1.2 &times; 10<sup>42</sup></td><td>6.4 &times; 10<sup>4</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J160211.7+155437</td><td>240.5491</td><td>15.9103</td><td>0.4</td><td>3.9 &times; 10<sup>-14</sup></td><td>159.2</td><td>S0<sup>0</sup></td><td>12.5</td><td>1.2 &times; 10<sup>41</sup></td><td>2.8 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J161249.8+540832</td><td>243.2076</td><td>54.1423</td><td>0.5</td><td>3.8 &times; 10<sup>-14</sup></td><td>711.2</td><td>E</td><td>14.8</td><td>2.3 &times; 10<sup>42</sup></td><td>4.6 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J162953.8+394601</td><td>247.4743</td><td>39.7670</td><td>6.2</td><td>4.1 &times; 10<sup>-14</sup></td><td>143.2</td><td>Sbc</td><td>21.2</td><td>1.0 &times; 10<sup>41</sup></td><td>1.7 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J163121.5-750652</td><td>247.8397</td><td>-75.1145</td><td>0.4</td><td>1.8 &times; 10<sup>-14</sup></td><td>498.9</td><td></td><td>57.1</td><td>5.3 &times; 10<sup>41</sup></td><td>8.5 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J163249.0+053852</td><td>248.2045</td><td>5.6479</td><td>0.5</td><td>7.1 &times; 10<sup>-15</sup></td><td>376.4</td><td></td><td>13.6</td><td>1.2 &times; 10<sup>41</sup></td><td>1.1 &times; 10<sup>4</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J164237.1+272634</td><td>250.6548</td><td>27.4428</td><td>0.4</td><td>3.1 &times; 10<sup>-14</sup></td><td>469.9</td><td>E</td><td>38.7</td><td>8.3 &times; 10<sup>41</sup></td><td>1.4 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J170932.2+342542</td><td>257.3845</td><td>34.4286</td><td>0.5</td><td>1.7 &times; 10<sup>-14</sup></td><td>353.2</td><td>Sc</td><td>9.5</td><td>2.6 &times; 10<sup>41</sup></td><td>4.7 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J171215.5+640212</td><td>258.0646</td><td>64.0368</td><td>0.5</td><td>1.1 &times; 10<sup>-14</sup></td><td>335.1</td><td>E</td><td>7.1</td><td>1.5 &times; 10<sup>41</sup></td><td>2.5 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr></tbody></table>

Notes. Column (1): name of the source. (2-4): source coordinates and position error. (5): broad-band mean X-ray flux. (6): galaxy distance. (7): galaxy morphology. (8): physical separation of the source to the galaxy centre. (9): broad-band mean X-ray luminosity. (10): black hole mass using the *r*-band luminosity and *g*–*r* colour (Bell et al. 2003). (11): galaxy mass given in GLADE+ (Dálya et al. 2022). (12): category assigned to the HLX in our study.
## Appendix A: List of candidates

The following tables present a partial sample of the ULXs and HLXs identified in this study. The full samples are available at the CDS.

<table><caption>**Table A.1.** List of HLX candidates obtained in this study.</caption><thead><tr><th>Name</th><th>RA deg</th><th>Dec deg</th><th>POSERR arcsec</th><th>F<sub>X</sub> erg cm<sup>-2</sup> s<sup>-1</sup></th><th>D Mpc</th><th>Gal. type</th><th>Sep. kpc</th><th>L<sub>X</sub> erg s<sup>-1</sup></th><th>M<sub>BH</sub> M<sub>☉</sub></th><th>M<sub>☉</sub>, Bell M<sub>☉</sub></th><th>Sub-sample</th></tr></thead><tbody><tr><td>2CXO J001143.2-285548</td><td>2.9303</td><td>-28.9301</td><td>1.1</td><td>1.4 &times; 10<sup>-14</sup></td><td>267.9</td><td>E</td><td>11.2</td><td>1.2 &times; 10<sup>41</sup></td><td>2.5 &times; 10<sup>4</sup></td><td>1.8 &times; 10<sup>7</sup></td><td>robust</td></tr><tr><td>2CXO J002234.1+001609</td><td>5.6424</td><td>0.2693</td><td>0.7</td><td>3.7 &times; 10<sup>-15</sup></td><td>485.3</td><td>S0<sup>0</sup></td><td>15.6</td><td>1.0 &times; 10<sup>41</sup></td><td>2.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J005151.7+474019</td><td>12.9658</td><td>47.6720</td><td>0.8</td><td>1.8 &times; 10<sup>-14</sup></td><td>682.5</td><td></td><td>16.7</td><td>10.0 &times; 10<sup>41</sup></td><td>1.9 &times; 10<sup>5</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J010739.2+541226</td><td>16.9134</td><td>54.2074</td><td>0.4</td><td>9.9 &times; 10<sup>-15</sup></td><td>497.8</td><td></td><td>14.3</td><td>2.9 &times; 10<sup>41</sup></td><td>4.1 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J011028.2-460422</td><td>17.6178</td><td>-46.0729</td><td>0.4</td><td>4.9 &times; 10<sup>-13</sup></td><td>90.9</td><td>S0<sup>+</sup></td><td>3.2</td><td>4.9 &times; 10<sup>41</sup></td><td></td><td></td><td>robust</td></tr><tr><td>2CXO J011751.9-265850</td><td>19.4664</td><td>-26.9808</td><td>1.3</td><td>8.5 &times; 10<sup>-15</sup></td><td>463.4</td><td></td><td>20.6</td><td>2.2 &times; 10<sup>41</sup></td><td>7.1 &times; 10<sup>4</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J011854.9-010551</td><td>19.7288</td><td>-1.0976</td><td>0.5</td><td>2.0 &times; 10<sup>-14</sup></td><td>557.2</td><td>E</td><td>13.4</td><td>7.5 &times; 10<sup>41</sup></td><td>1.2 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J023659.5-511548</td><td>39.2481</td><td>-51.2636</td><td>2.8</td><td>4.7 &times; 10<sup>-14</sup></td><td>343.6</td><td></td><td>24.6</td><td>6.6 &times; 10<sup>41</sup></td><td>1.1 &times; 10<sup>5</sup></td><td>5.8 &times; 10<sup>7</sup></td><td>robust</td></tr><tr><td>2CXO J024106.1-081711</td><td>40.2757</td><td>-8.2865</td><td>0.6</td><td>3.3 &times; 10<sup>-15</sup></td><td>636.8</td><td></td><td>24.6</td><td>1.6 &times; 10<sup>41</sup></td><td>2.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J024228.5-000202</td><td>40.6188</td><td>-0.0340</td><td>0.4</td><td>7.1 &times; 10<sup>-15</sup></td><td>691.8</td><td>E</td><td>27.3</td><td>4.1 &times; 10<sup>41</sup></td><td>8.8 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J025843.0-523930</td><td>44.6794</td><td>-52.6584</td><td>0.5</td><td>4.7 &times; 10<sup>-15</sup></td><td>428.3</td><td></td><td>9.5</td><td>1.0 &times; 10<sup>41</sup></td><td></td><td></td><td>robust</td></tr><tr><td>2CXO J025921.5+132913</td><td>44.8398</td><td>13.4871</td><td>0.6</td><td>8.0 &times; 10<sup>-15</sup></td><td>487.5</td><td></td><td>8.2</td><td>2.3 &times; 10<sup>41</sup></td><td>3.0 &times; 10<sup>4</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J031049.4-265431</td><td>47.7062</td><td>-26.9088</td><td>0.8</td><td>2.0 &times; 10<sup>-14</sup></td><td>597.0</td><td></td><td>14.8</td><td>8.6 &times; 10<sup>41</sup></td><td>1.6 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J034115.1+152335</td><td>55.3129</td><td>15.3932</td><td>0.4</td><td>2.7 &times; 10<sup>-14</sup></td><td>184.4</td><td></td><td>3.8</td><td>1.1 &times; 10<sup>41</sup></td><td>1.5 &times; 10<sup>4</sup></td><td>3.5 &times; 10<sup>7</sup></td><td>weak</td></tr><tr><td>2CXO J034231.8-533841</td><td>55.6325</td><td>-53.6449</td><td>0.4</td><td>2.3 &times; 10<sup>-14</sup></td><td>270.4</td><td>E</td><td>12.2</td><td>2.0 &times; 10<sup>41</sup></td><td>3.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J041338.6+102803</td><td>63.4112</td><td>10.4678</td><td>0.5</td><td>6.0 &times; 10<sup>-15</sup></td><td>405.5</td><td></td><td>10.7</td><td>1.2 &times; 10<sup>41</sup></td><td>1.7 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J043338.4-131612</td><td>68.4101</td><td>-13.2702</td><td>0.4</td><td>5.2 &times; 10<sup>-14</sup></td><td>141.9</td><td>S0<sup>-</sup></td><td>19.8</td><td>1.2 &times; 10<sup>41</sup></td><td>2.0 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J044921.6-485545</td><td>72.3403</td><td>-48.9294</td><td>0.9</td><td>6.7 &times; 10<sup>-15</sup></td><td>355.9</td><td></td><td>6.7</td><td>1.0 &times; 10<sup>41</sup></td><td>1.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J055107.0-570640</td><td>87.7793</td><td>-57.1111</td><td>0.5</td><td>1.5 &times; 10<sup>-14</sup></td><td>267.9</td><td></td><td>15.3</td><td>1.3 &times; 10<sup>41</sup></td><td>2.9 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J061620.8-215616</td><td>94.0867</td><td>-21.9379</td><td>0.5</td><td>1.8 &times; 10<sup>-14</sup></td><td>1.0 &times; 10<sup>3</sup></td><td></td><td>13.2</td><td>2.3 &times; 10<sup>42</sup></td><td>2.1 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J062648.6-543208</td><td>96.7028</td><td>-54.5357</td><td>0.4</td><td>7.5 &times; 10<sup>-14</sup></td><td>225.9</td><td>E</td><td>27.9</td><td>4.6 &times; 10<sup>41</sup></td><td>4.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J071051.5-561009</td><td>107.7150</td><td>-56.1694</td><td>0.8</td><td>1.9 &times; 10<sup>-14</sup></td><td>562.3</td><td></td><td>14.3</td><td>7.2 &times; 10<sup>41</sup></td><td>1.3 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J071644.9+372828</td><td>109.1875</td><td>37.4746</td><td>1.3</td><td>2.5 &times; 10<sup>-14</sup></td><td>317.9</td><td></td><td>14.0</td><td>3.0 &times; 10<sup>41</sup></td><td>4.0 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J074735.8+554113</td><td>116.8994</td><td>55.6870</td><td>0.5</td><td>4.0 &times; 10<sup>-14</sup></td><td>152.1</td><td></td><td>4.2</td><td>1.1 &times; 10<sup>41</sup></td><td>1.6 &times; 10<sup>4</sup></td><td>2.5 &times; 10<sup>9</sup></td><td>weak</td></tr><tr><td>2CXO J081654.4-073931</td><td>124.2271</td><td>-7.6588</td><td>1.4</td><td>1.3 &times; 10<sup>-14</sup></td><td>311.2</td><td></td><td>13.7</td><td>1.5 &times; 10<sup>41</sup></td><td>2.8 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J082213.9+210535</td><td>125.5665</td><td>21.0933</td><td>0.5</td><td>1.2 &times; 10<sup>-13</sup></td><td>92.3</td><td>S0<sup>-</sup></td><td>1.9</td><td>1.2 &times; 10<sup>41</sup></td><td>2.2 &times; 10<sup>4</sup></td><td>3.0 &times; 10<sup>10</sup></td><td>robust</td></tr><tr><td>2CXO J084128.8+322447</td><td>130.3700</td><td>32.4133</td><td>0.4</td><td>1.2 &times; 10<sup>-14</sup></td><td>295.1</td><td>S0<sup>0</sup></td><td>11.4</td><td>1.3 &times; 10<sup>41</sup></td><td>2.4 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J084135.0+010156</td><td>130.3962</td><td>1.0323</td><td>0.4</td><td>6.6 &times; 10<sup>-14</sup></td><td>503.5</td><td></td><td>7.0</td><td>2.0 &times; 10<sup>42</sup></td><td>3.8 &times; 10<sup>5</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J091449.0+085321</td><td>138.7045</td><td>8.8892</td><td>0.4</td><td>6.8 &times; 10<sup>-13</sup></td><td>648.6</td><td>E</td><td>7.9</td><td>3.4 &times; 10<sup>43</sup></td><td>1.7 &times; 10<sup>7</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J101239.8-010628</td><td>153.1662</td><td>-1.1078</td><td>0.5</td><td>9.5 &times; 10<sup>-15</sup></td><td>438.5</td><td>Sa</td><td>9.4</td><td>2.2 &times; 10<sup>41</sup></td><td>4.1 &times; 10<sup>4</sup></td><td>2.6 &times; 10<sup>4</sup></td><td>galaxy pair</td></tr><tr><td>2CXO J103619.8-273939</td><td>159.0827</td><td>-27.6610</td><td>0.9</td><td>8.6 &times; 10<sup>-15</sup></td><td>430.5</td><td>S0<sup>+</sup></td><td>27.1</td><td>1.9 &times; 10<sup>41</sup></td><td>2.9 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J103844.2+485220</td><td>159.6845</td><td>48.8724</td><td>0.4</td><td>9.2 &times; 10<sup>-15</sup></td><td>539.5</td><td></td><td>13.9</td><td>3.2 &times; 10<sup>41</sup></td><td>5.4 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J104142.2+400035</td><td>160.4262</td><td>40.0098</td><td>0.9</td><td>1.5 &times; 10<sup>-14</sup></td><td>642.7</td><td></td><td>24.7</td><td>7.6 &times; 10<sup>41</sup></td><td></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J105210.4+552243</td><td>163.0435</td><td>55.3786</td><td>0.5</td><td>6.9 &times; 10<sup>-15</sup></td><td>669.9</td><td>Sb</td><td>12.2</td><td>3.7 &times; 10<sup>41</sup></td><td>5.7 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J111610.0+013035</td><td>169.0418</td><td>1.5098</td><td>0.5</td><td>1.7 &times; 10<sup>-14</sup></td><td>500.9</td><td>Sbc</td><td>11.9</td><td>5.2 &times; 10<sup>41</sup></td><td>1.1 &times; 10<sup>5</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J112002.6+132830</td><td>170.0112</td><td>13.4752</td><td>2.0</td><td>4.2 &times; 10<sup>-15</sup></td><td>586.1</td><td>Sc</td><td>20.6</td><td>1.7 &times; 10<sup>41</sup></td><td>2.2 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J112110.9-232331</td><td>170.2958</td><td>23.3922</td><td>0.6</td><td>4.2 &times; 10<sup>-15</sup></td><td>513.2</td><td>E</td><td>13.1</td><td>1.3 &times; 10<sup>41</sup></td><td>2.5 &times; 10<sup>4</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J112255.5+010601</td><td>170.7313</td><td>1.1004</td><td>0.4</td><td>2.4 &times; 10<sup>-14</sup></td><td>342.0</td><td>E</td><td>17.5</td><td>3.4 &times; 10<sup>41</sup></td><td>8.1 &times; 10<sup>4</sup></td><td>3.3 &times; 10<sup>8</sup></td><td>weak</td></tr><tr><td>2CXO J121756.3+280941</td><td>184.4849</td><td>28.1615</td><td>0.5</td><td>1.2 &times; 10<sup>-14</sup></td><td>613.8</td><td>E</td><td>17.1</td><td>5.3 &times; 10<sup>41</sup></td><td>1.1 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J122155.1+271022</td><td>185.4796</td><td>27.1728</td><td>0.4</td><td>1.2 &times; 10<sup>-14</sup></td><td>363.1</td><td>E</td><td>6.4</td><td>1.9 &times; 10<sup>41</sup></td><td>2.0 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J123307.6+091942</td><td>188.2820</td><td>9.3285</td><td>0.6</td><td>3.3 &times; 10<sup>-14</sup></td><td>309.0</td><td>Sd</td><td>6.1</td><td>3.7 &times; 10<sup>41</sup></td><td>8.0 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J123605.6+163213</td><td>189.0235</td><td>16.5370</td><td>1.4</td><td>9.7 &times; 10<sup>-15</sup></td><td>318.0</td><td>E</td><td>12.5</td><td>1.2 &times; 10<sup>41</sup></td><td>1.3 &times; 10<sup>4</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J124208.4+331854</td><td>190.5351</td><td>33.3151</td><td>0.4</td><td>8.9 &times; 10<sup>-14</sup></td><td>701.9</td><td>E</td><td>15.2</td><td>5.3 &times; 10<sup>42</sup></td><td>1.3 &times; 10<sup>6</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J130155.9+291815</td><td>195.4833</td><td>29.3044</td><td>1.2</td><td>1.8 &times; 10<sup>-14</sup></td><td>776.2</td><td></td><td>30.3</td><td>1.3 &times; 10<sup>42</sup></td><td></td><td></td><td>robust</td></tr><tr><td>2CXO J131133.3-011656</td><td>197.8891</td><td>-1.2824</td><td>0.4</td><td>6.6 &times; 10<sup>-15</sup></td><td>895.4</td><td></td><td>22.3</td><td>6.3 &times; 10<sup>41</sup></td><td>1.2 &times; 10<sup>5</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J131619.4+620610</td><td>199.0809</td><td>62.1029</td><td>0.9</td><td>1.4 &times; 10<sup>-14</sup></td><td>610.9</td><td>E</td><td>14.4</td><td>6.1 &times; 10<sup>41</sup></td><td>9.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J132519.7-313607</td><td>201.3324</td><td>-31.6021</td><td>0.4</td><td>5.5 &times; 10<sup>-14</sup></td><td>214.8</td><td></td><td>4.0</td><td>3.0 &times; 10<sup>41</sup></td><td>8.1 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J133338.8-314045</td><td>203.4120</td><td>-31.6792</td><td>0.5</td><td>2.3 &times; 10<sup>-14</sup></td><td>214.8</td><td>S0<sup>+</sup></td><td>55.0</td><td>1.3 &times; 10<sup>41</sup></td><td>2.2 &times; 10<sup>3</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J134736.4+173404</td><td>206.9018</td><td>17.5680</td><td>0.4</td><td>3.2 &times; 10<sup>-13</sup></td><td>199.2</td><td>Sbc</td><td>8.2</td><td>1.5 &times; 10<sup>42</sup></td><td>4.5 &times; 10<sup>5</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J140155.7-113809</td><td>210.4823</td><td>-11.6360</td><td>0.4</td><td>3.2 &times; 10<sup>-14</sup></td><td>230.3</td><td></td><td>5.4</td><td>2.0 &times; 10<sup>41</sup></td><td>3.1 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J142010.7+533348</td><td>215.0448</td><td>53.5635</td><td>0.6</td><td>1.2 &times; 10<sup>-14</sup></td><td>293.8</td><td>Irr</td><td>8.3</td><td>1.2 &times; 10<sup>41</sup></td><td>1.6 &times; 10<sup>4</sup></td><td>2.1 &times; 10<sup>6</sup></td><td>robust</td></tr><tr><td>2CXO J145409.9+183700</td><td>223.5415</td><td>18.6169</td><td>1.6</td><td>4.0 &times; 10<sup>-15</sup></td><td>520.0</td><td>Sc</td><td>24.2</td><td>1.3 &times; 10<sup>41</sup></td><td>2.3 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J150930.4+333330</td><td>227.3769</td><td>33.5585</td><td>0.6</td><td>3.1 &times; 10<sup>-14</sup></td><td>1.0 &times; 10<sup>3</sup></td><td></td><td>24.3</td><td>4.0 &times; 10<sup>42</sup></td><td>9.3 &times; 10<sup>5</sup></td><td>5.5 &times; 10<sup>9</sup></td><td>weak</td></tr><tr><td>2CXO J150940.1+333033</td><td>227.4172</td><td>33.5094</td><td>0.6</td><td>7.6 &times; 10<sup>-15</sup></td><td>549.5</td><td>E</td><td>13.4</td><td>2.8 &times; 10<sup>41</sup></td><td>6.9 &times; 10<sup>4</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J152435.6+295302</td><td>231.1486</td><td>29.8841</td><td>0.7</td><td>3.2 &times; 10<sup>-15</sup></td><td>557.2</td><td></td><td>14.7</td><td>1.2 &times; 10<sup>41</sup></td><td>4.5 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J153143.2+240421</td><td>232.9304</td><td>24.0725</td><td>0.4</td><td>5.7 &times; 10<sup>-14</sup></td><td>438.5</td><td>Sab</td><td>5.9</td><td>1.2 &times; 10<sup>42</sup></td><td>6.4 &times; 10<sup>4</sup></td><td></td><td>galaxy pair</td></tr><tr><td>2CXO J160211.7+155437</td><td>240.5491</td><td>15.9103</td><td>0.4</td><td>3.9 &times; 10<sup>-14</sup></td><td>159.2</td><td>S0<sup>0</sup></td><td>12.5</td><td>1.2 &times; 10<sup>41</sup></td><td>2.8 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J161249.8+540832</td><td>243.2076</td><td>54.1423</td><td>0.5</td><td>3.8 &times; 10<sup>-14</sup></td><td>711.2</td><td>E</td><td>14.8</td><td>2.3 &times; 10<sup>42</sup></td><td>4.6 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J162953.8+394601</td><td>247.4743</td><td>39.7670</td><td>6.2</td><td>4.1 &times; 10<sup>-14</sup></td><td>143.2</td><td>Sbc</td><td>21.2</td><td>1.0 &times; 10<sup>41</sup></td><td>1.7 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J163121.5-750652</td><td>247.8397</td><td>-75.1145</td><td>0.4</td><td>1.8 &times; 10<sup>-14</sup></td><td>498.9</td><td></td><td>57.1</td><td>5.3 &times; 10<sup>41</sup></td><td>8.5 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J163249.0+053852</td><td>248.2045</td><td>5.6479</td><td>0.5</td><td>7.1 &times; 10<sup>-15</sup></td><td>376.4</td><td></td><td>13.6</td><td>1.2 &times; 10<sup>41</sup></td><td>1.1 &times; 10<sup>4</sup></td><td></td><td>weak</td></tr><tr><td>2CXO J164237.1+272634</td><td>250.6548</td><td>27.4428</td><td>0.4</td><td>3.1 &times; 10<sup>-14</sup></td><td>469.9</td><td>E</td><td>38.7</td><td>8.3 &times; 10<sup>41</sup></td><td>1.4 &times; 10<sup>5</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J170932.2+342542</td><td>257.3845</td><td>34.4286</td><td>0.5</td><td>1.7 &times; 10<sup>-14</sup></td><td>353.2</td><td>Sc</td><td>9.5</td><td>2.6 &times; 10<sup>41</sup></td><td>4.7 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr><tr><td>2CXO J171215.5+640212</td><td>258.0646</td><td>64.0368</td><td>0.5</td><td>1.1 &times; 10<sup>-14</sup></td><td>335.1</td><td>E</td><td>7.1</td><td>1.5 &times; 10<sup>41</sup></td><td>2.5 &times; 10<sup>4</sup></td><td></td><td>robust</td></tr></tbody></table>

Notes. Column (1): name of the source. (2-4): source coordinates and position error. (5): broad-band mean X-ray flux. (6): galaxy distance. (7): galaxy morphology. (8): physical separation of the source to the galaxy centre. (9): broad-band mean X-ray luminosity. (10): black hole mass using the *r*-band luminosity and *g*-*r* colour (Bell et al. 2003). (11): galaxy mass given in GLADE+ (Dálya et al. 2022). (12): category assigned to the HLX in our study.
<table><caption>**Table A.2.** List of ULX candidates obtained in this study.</caption><thead><tr><th>Name</th><th>RA deg</th><th>Dec deg</th><th>POSERR arcsec</th><th>F<sub>X</sub> erg cm<sup>-2</sup> s<sup>-1</sup></th><th>D Mpc</th><th>Gal. type</th><th>Sep. kpc</th><th>L<sub>X</sub> erg s<sup>-1</sup></th><th>P<sub>XRB</sub></th><th>f<sub>cont</sub></th></tr></thead><tbody><tr><td>2CXO J000120.2+130641</td><td>0.3342</td><td>13.1114</td><td>0.4</td><td>5.5 &times; 10<sup>-15</sup></td><td>76.5</td><td>S0/E</td><td>1.3</td><td>3.9 &times; 10<sup>39</sup></td><td>0.56</td><td>0.01</td></tr><tr><td>2CXO J000125.1+130708</td><td>0.3549</td><td>13.1189</td><td>0.5</td><td>2.0 &times; 10<sup>-15</sup></td><td>75.0</td><td>S</td><td>8.8</td><td>1.3 &times; 10<sup>39</sup></td><td>0.41</td><td>0.20</td></tr><tr><td>2CXO J000126.7+130649</td><td>0.3616</td><td>13.1136</td><td>0.5</td><td>8.3 &times; 10<sup>-15</sup></td><td>75.0</td><td>S</td><td>3.9</td><td>5.6 &times; 10<sup>39</sup></td><td>0.82</td><td>0.08</td></tr><tr><td>2CXO J000141.1+232949</td><td>0.4215</td><td>23.4972</td><td>0.4</td><td>2.8 &times; 10<sup>-15</sup></td><td>62.5</td><td>S</td><td>3.4</td><td>1.3 &times; 10<sup>39</sup></td><td>0.55</td><td>0.02</td></tr><tr><td>2CXO J000142.3+232941</td><td>0.4263</td><td>23.4947</td><td>0.4</td><td>3.9 &times; 10<sup>-15</sup></td><td>62.5</td><td>S</td><td>1.9</td><td>1.8 &times; 10<sup>39</sup></td><td>0.43</td><td>0.00</td></tr><tr><td>2CXO J000142.9+232935</td><td>0.4290</td><td>23.4933</td><td>0.4</td><td>3.9 &times; 10<sup>-15</sup></td><td>62.5</td><td>S</td><td>5.0</td><td>1.8 &times; 10<sup>39</sup></td><td>0.80</td><td>0.02</td></tr><tr><td>2CXO J000254.5-354308</td><td>0.7274</td><td>-35.7189</td><td>0.5</td><td>4.9 &times; 10<sup>-15</sup></td><td>212.8</td><td>S0/E</td><td>10.6</td><td>2.6 &times; 10<sup>40</sup></td><td>0.56</td><td>0.40</td></tr><tr><td>2CXO J000619.5-413019</td><td>1.5814</td><td>-41.5054</td><td>0.4</td><td>2.3 &times; 10<sup>-14</sup></td><td>19.5</td><td>S</td><td>1.9</td><td>1.1 &times; 10<sup>39</sup></td><td>0.58</td><td>0.00</td></tr><tr><td>2CXO J000620.2-413005</td><td>1.5842</td><td>-41.5016</td><td>0.4</td><td>8.9 &times; 10<sup>-14</sup></td><td>19.5</td><td>S</td><td>0.7</td><td>4.0 &times; 10<sup>39</sup></td><td>0.44</td><td>0.00</td></tr><tr><td>2CXO J000952.9+255547</td><td>2.4708</td><td>25.9299</td><td>0.5</td><td>4.4 &times; 10<sup>-15</sup></td><td>65.8</td><td>S</td><td>7.1</td><td>2.3 &times; 10<sup>39</sup></td><td></td><td></td></tr><tr><td>2CXO J000953.2+255454</td><td>2.4720</td><td>25.9153</td><td>0.5</td><td>2.1 &times; 10<sup>-15</sup></td><td>65.8</td><td>S</td><td>9.5</td><td>1.1 &times; 10<sup>39</sup></td><td>0.83</td><td>0.29</td></tr><tr><td>2CXO J000955.1+255536</td><td>2.4800</td><td>25.9267</td><td>0.7</td><td>2.5 &times; 10<sup>-15</sup></td><td>65.8</td><td>S</td><td>8.1</td><td>1.3 &times; 10<sup>39</sup></td><td>0.75</td><td>0.32</td></tr><tr><td>2CXO J001106.9-120631</td><td>2.7788</td><td>-12.1088</td><td>0.4</td><td>8.7 &times; 10<sup>-15</sup></td><td>83.3</td><td>S</td><td>2.2</td><td>7.2 &times; 10<sup>39</sup></td><td>0.25</td><td>0.09</td></tr><tr><td>2CXO J001815.4+300343</td><td>4.5646</td><td>30.0620</td><td>0.7</td><td>1.9 &times; 10<sup>-15</sup></td><td>93.9</td><td>S0/E</td><td>4.3</td><td>2.0 &times; 10<sup>39</sup></td><td>0.59</td><td>0.13</td></tr><tr><td>2CXO J001827.1+300210</td><td>4.6131</td><td>30.0363</td><td>0.5</td><td>6.7 &times; 10<sup>-15</sup></td><td>106.7</td><td>S</td><td>11.1</td><td>9.1 &times; 10<sup>39</sup></td><td>0.63</td><td>0.34</td></tr><tr><td>2CXO J001849.8-102134</td><td>4.7077</td><td>-10.3596</td><td>0.4</td><td>9.7 &times; 10<sup>-15</sup></td><td>116.4</td><td>S</td><td>4.5</td><td>1.6 &times; 10<sup>40</sup></td><td>0.43</td><td>0.28</td></tr><tr><td>2CXO J001850.4-102228</td><td>4.7102</td><td>-10.3746</td><td>0.4</td><td>4.8 &times; 10<sup>-15</sup></td><td>119.7</td><td>S</td><td>5.7</td><td>8.2 &times; 10<sup>39</sup></td><td>0.58</td><td>0.05</td></tr><tr><td>2CXO J001850.9-102232</td><td>4.7122</td><td>-10.3757</td><td>0.5</td><td>1.1 &times; 10<sup>-14</sup></td><td>119.7</td><td>S</td><td>2.2</td><td>1.8 &times; 10<sup>40</sup></td><td>0.57</td><td>0.01</td></tr><tr><td>2CXO J001850.9-102249</td><td>4.7125</td><td>-10.3804</td><td>0.5</td><td>1.8 &times; 10<sup>-15</sup></td><td>119.7</td><td>S</td><td>7.1</td><td>3.0 &times; 10<sup>39</sup></td><td>0.76</td><td>0.12</td></tr><tr><td>2CXO J001851.2-102244</td><td>4.7134</td><td>-10.3791</td><td>0.4</td><td>7.5 &times; 10<sup>-15</sup></td><td>119.7</td><td>S</td><td>5.1</td><td>1.3 &times; 10<sup>40</sup></td><td>0.56</td><td>0.05</td></tr><tr><td>2CXO J002751.6-014813</td><td>6.9653</td><td>-1.8037</td><td>2.7</td><td>1.4 &times; 10<sup>-13</sup></td><td>57.6</td><td>S</td><td>6.9</td><td>5.4 &times; 10<sup>40</sup></td><td>0.30</td><td>0.24</td></tr><tr><td>2CXO J003358.1-094222</td><td>8.4922</td><td>-9.7062</td><td>0.5</td><td>1.2 &times; 10<sup>-14</sup></td><td>52.9</td><td>S</td><td>17.2</td><td>4.2 &times; 10<sup>39</sup></td><td>0.75</td><td>0.54</td></tr><tr><td>2CXO J003404.3-094248</td><td>8.5182</td><td>-9.7133</td><td>0.5</td><td>1.1 &times; 10<sup>-14</sup></td><td>52.9</td><td>S</td><td>9.3</td><td>3.7 &times; 10<sup>39</sup></td><td>0.79</td><td>0.35</td></tr><tr><td>2CXO J003404.5-094239</td><td>8.5191</td><td>-9.7110</td><td>0.6</td><td>7.8 &times; 10<sup>-15</sup></td><td>52.9</td><td>S</td><td>8.4</td><td>2.6 &times; 10<sup>39</sup></td><td>0.41</td><td>0.24</td></tr><tr><td>2CXO J003408.4-094140</td><td>8.5351</td><td>-9.6947</td><td>1.2</td><td>1.3 &times; 10<sup>-14</sup></td><td>67.8</td><td>S</td><td>2.6</td><td>7.1 &times; 10<sup>39</sup></td><td>0.29</td><td>0.02</td></tr><tr><td>2CXO J003413.6-212803</td><td>8.5568</td><td>-21.4676</td><td>0.7</td><td>1.5 &times; 10<sup>-15</sup></td><td>96.3</td><td>S</td><td>4.7</td><td>1.7 &times; 10<sup>39</sup></td><td>0.61</td><td>0.09</td></tr><tr><td>2CXO J003414.9-212455</td><td>8.5622</td><td>-21.4155</td><td>0.5</td><td>1.8 &times; 10<sup>-15</sup></td><td>270.4</td><td>S0/E</td><td>12.6</td><td>1.6 &times; 10<sup>40</sup></td><td>0.84</td><td>0.18</td></tr><tr><td>2CXO J003416.0-212517</td><td>8.5669</td><td>-21.4215</td><td>0.4</td><td>2.7 &times; 10<sup>-15</sup></td><td>270.4</td><td>S0/E</td><td>18.9</td><td>2.4 &times; 10<sup>40</sup></td><td>0.60</td><td>0.46</td></tr><tr><td>2CXO J003654.5-010737</td><td>9.2271</td><td>-1.1271</td><td>1.1</td><td>1.4 &times; 10<sup>-15</sup></td><td>326.6</td><td>S</td><td>9.8</td><td>1.7 &times; 10<sup>40</sup></td><td>0.26</td><td>0.23</td></tr><tr><td>2CXO J003703.9-010904</td><td>9.2665</td><td>-1.1514</td><td>0.4</td><td>1.0 &times; 10<sup>-14</sup></td><td>328.1</td><td>S0/E</td><td>5.2</td><td>1.3 &times; 10<sup>41</sup></td><td>0.24</td><td>0.07</td></tr><tr><td>2CXO J003737.5-334255</td><td>9.4067</td><td>-33.7153</td><td>0.4</td><td>6.3 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>25.5</td><td>1.2 &times; 10<sup>40</sup></td><td></td><td></td></tr><tr><td>2CXO J003738.1-334306</td><td>9.4088</td><td>-33.7183</td><td>0.4</td><td>9.0 &times; 10<sup>-16</sup></td><td>126.5</td><td>S</td><td>22.2</td><td>1.7 &times; 10<sup>39</sup></td><td>0.67</td><td>0.15</td></tr><tr><td>2CXO J003738.3-334309</td><td>9.4098</td><td>-33.7192</td><td>0.4</td><td>1.0 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>20.8</td><td>1.9 &times; 10<sup>39</sup></td><td>0.61</td><td>0.13</td></tr><tr><td>2CXO J003738.7-334316</td><td>9.4114</td><td>-33.7212</td><td>0.4</td><td>7.5 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>20.0</td><td>1.4 &times; 10<sup>40</sup></td><td>0.37</td><td>0.13</td></tr><tr><td>2CXO J003739.1-334229</td><td>9.4131</td><td>-33.7083</td><td>0.4</td><td>2.9 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>22.0</td><td>5.6 &times; 10<sup>39</sup></td><td>0.75</td><td>0.13</td></tr><tr><td>2CXO J003739.2-334250</td><td>9.4134</td><td>-33.7139</td><td>0.4</td><td>4.4 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>14.6</td><td>8.5 &times; 10<sup>39</sup></td><td>0.83</td><td>0.06</td></tr><tr><td>2CXO J003739.3-334323</td><td>9.4141</td><td>-33.7231</td><td>0.4</td><td>2.6 &times; 10<sup>-14</sup></td><td>126.5</td><td>S</td><td>18.9</td><td>5.0 &times; 10<sup>40</sup></td><td>0.38</td><td>0.11</td></tr><tr><td>2CXO J003740.2-334327</td><td>9.4177</td><td>-33.7242</td><td>0.4</td><td>1.5 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>17.6</td><td>2.9 &times; 10<sup>39</sup></td><td>0.32</td><td>0.10</td></tr><tr><td>2CXO J003740.4-334324</td><td>9.4185</td><td>-33.7236</td><td>0.4</td><td>1.0 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>15.9</td><td>2.0 &times; 10<sup>39</sup></td><td>0.66</td><td>0.08</td></tr><tr><td>2CXO J003740.7-334258</td><td>9.4198</td><td>-33.7161</td><td>0.4</td><td>5.3 &times; 10<sup>-16</sup></td><td>126.5</td><td>S</td><td>2.7</td><td>1.0 &times; 10<sup>39</sup></td><td>0.53</td><td>0.00</td></tr><tr><td>2CXO J003740.8-334331</td><td>9.4203</td><td>-33.7253</td><td>0.4</td><td>4.1 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>18.8</td><td>7.8 &times; 10<sup>39</sup></td><td>0.56</td><td>0.11</td></tr><tr><td>2CXO J003741.2-334232</td><td>9.4218</td><td>-33.7090</td><td>0.4</td><td>1.3 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>15.4</td><td>2.6 &times; 10<sup>39</sup></td><td>0.83</td><td>0.07</td></tr><tr><td>2CXO J003741.3-334331</td><td>9.4223</td><td>-33.7254</td><td>0.4</td><td>8.9 &times; 10<sup>-16</sup></td><td>126.5</td><td>S</td><td>19.0</td><td>1.7 &times; 10<sup>39</sup></td><td>0.68</td><td>0.11</td></tr><tr><td>2CXO J003742.4-334249</td><td>9.4267</td><td>-33.7138</td><td>0.4</td><td>3.7 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>10.8</td><td>7.1 &times; 10<sup>39</sup></td><td>0.70</td><td>0.04</td></tr><tr><td>2CXO J003742.4-334304</td><td>9.4270</td><td>-33.7178</td><td>0.4</td><td>9.1 &times; 10<sup>-16</sup></td><td>126.5</td><td>S</td><td>10.4</td><td>1.7 &times; 10<sup>39</sup></td><td>0.81</td><td>0.03</td></tr><tr><td>2CXO J003742.7-334212</td><td>9.4283</td><td>-33.7035</td><td>0.4</td><td>1.1 &times; 10<sup>-15</sup></td><td>128.2</td><td>S</td><td>6.7</td><td>2.3 &times; 10<sup>39</sup></td><td>0.87</td><td>0.03</td></tr><tr><td>2CXO J003742.8-334314</td><td>9.4286</td><td>-33.7207</td><td>0.4</td><td>8.7 &times; 10<sup>-16</sup></td><td>126.5</td><td>S</td><td>15.6</td><td>1.7 &times; 10<sup>39</sup></td><td>0.80</td><td>0.07</td></tr><tr><td>2CXO J003742.9-334204</td><td>9.4289</td><td>-33.7012</td><td>0.4</td><td>2.4 &times; 10<sup>-15</sup></td><td>128.2</td><td>S</td><td>4.7</td><td>4.8 &times; 10<sup>39</sup></td><td>0.63</td><td>0.01</td></tr><tr><td>2CXO J003743.8-334209</td><td>9.4327</td><td>-33.7028</td><td>0.4</td><td>2.4 &times; 10<sup>-15</sup></td><td>128.2</td><td>S</td><td>3.0</td><td>4.7 &times; 10<sup>39</sup></td><td>0.69</td><td>0.01</td></tr><tr><td>2CXO J003745.3-334228</td><td>9.4388</td><td>-33.7079</td><td>0.4</td><td>2.2 &times; 10<sup>-15</sup></td><td>155.4</td><td>S0/E</td><td>6.3</td><td>6.3 &times; 10<sup>39</sup></td><td>0.82</td><td>0.20</td></tr><tr><td>2CXO J003747.0-333953</td><td>9.4459</td><td>-33.6647</td><td>0.5</td><td>1.8 &times; 10<sup>-15</sup></td><td>127.9</td><td>S</td><td>5.5</td><td>3.6 &times; 10<sup>39</sup></td><td>0.70</td><td>0.07</td></tr><tr><td>2CXO J003912.0+005153</td><td>9.8000</td><td>0.8650</td><td>1.2</td><td>2.7 &times; 10<sup>-15</sup></td><td>59.7</td><td>S</td><td>5.9</td><td>1.1 &times; 10<sup>39</sup></td><td>0.74</td><td>0.31</td></tr><tr><td>2CXO J003913.2+005142</td><td>9.8051</td><td>0.8617</td><td>0.5</td><td>2.9 &times; 10<sup>-14</sup></td><td>59.7</td><td>S</td><td>2.6</td><td>1.2 &times; 10<sup>40</sup></td><td>0.68</td><td>0.03</td></tr><tr><td>2CXO J003917.1+031940</td><td>9.8214</td><td>3.3279</td><td>0.4</td><td>3.4 &times; 10<sup>-15</sup></td><td>61.6</td><td>S0/E</td><td>7.2</td><td>1.5 &times; 10<sup>39</sup></td><td>0.70</td><td>0.10</td></tr><tr><td>2CXO J003919.7+031945</td><td>9.8324</td><td>3.3294</td><td>0.4</td><td>4.2 &times; 10<sup>-15</sup></td><td>61.6</td><td>S0/E</td><td>5.6</td><td>1.9 &times; 10<sup>39</sup></td><td>0.83</td><td>0.10</td></tr></tbody></table>

**Notes.** Column (1): name of the source. (2–4): source coordinates and position error. (5): broad-band mean X-ray flux. (6): galaxy distance. (7): galaxy morphology. (8): physical separation of the source to the galaxy centre. (9): broad-band mean X-ray luminosity. (10): probability that the source is an XRB, given by the classifier. (11) fraction of ULX candidates being background contaminants within the separation of the ULX, given by the log N − log S method.
<table><caption>**Table A.2.** List of ULX candidates obtained in this study.</caption><thead><tr><th>Name</th><th>RA deg</th><th>Dec deg</th><th>POSERR arcsec</th><th>F<sub>X</sub> erg cm<sup>-2</sup> s<sup>-1</sup></th><th>D Mpc</th><th>Gal. type</th><th>Sep. kpc</th><th>L<sub>X</sub> erg s<sup>-1</sup></th><th>P<sub>XRB</sub></th><th>f<sub>cont</sub></th></tr></thead><tbody><tr><td>2CXO J000120.2+130641</td><td>0.3342</td><td>13.1114</td><td>0.4</td><td>5.5 &times; 10<sup>-15</sup></td><td>76.5</td><td>S0/E</td><td>1.3</td><td>3.9 &times; 10<sup>39</sup></td><td>0.56</td><td>0.01</td></tr><tr><td>2CXO J000125.1+130708</td><td>0.3549</td><td>13.1189</td><td>0.5</td><td>2.0 &times; 10<sup>-15</sup></td><td>75.0</td><td>S</td><td>8.8</td><td>1.3 &times; 10<sup>39</sup></td><td>0.41</td><td>0.20</td></tr><tr><td>2CXO J000126.7+130649</td><td>0.3616</td><td>13.1136</td><td>0.5</td><td>8.3 &times; 10<sup>-15</sup></td><td>75.0</td><td>S</td><td>3.9</td><td>5.6 &times; 10<sup>39</sup></td><td>0.82</td><td>0.08</td></tr><tr><td>2CXO J000141.1+232949</td><td>0.4215</td><td>23.4972</td><td>0.4</td><td>2.8 &times; 10<sup>-15</sup></td><td>62.5</td><td>S</td><td>3.4</td><td>1.3 &times; 10<sup>39</sup></td><td>0.55</td><td>0.02</td></tr><tr><td>2CXO J000142.3+232941</td><td>0.4263</td><td>23.4947</td><td>0.4</td><td>3.9 &times; 10<sup>-15</sup></td><td>62.5</td><td>S</td><td>1.9</td><td>1.8 &times; 10<sup>39</sup></td><td>0.43</td><td>0.00</td></tr><tr><td>2CXO J000142.9+232935</td><td>0.4290</td><td>23.4933</td><td>0.4</td><td>3.9 &times; 10<sup>-15</sup></td><td>62.5</td><td>S</td><td>5.0</td><td>1.8 &times; 10<sup>39</sup></td><td>0.80</td><td>0.02</td></tr><tr><td>2CXO J000254.5-354308</td><td>0.7274</td><td>-35.7189</td><td>0.5</td><td>4.9 &times; 10<sup>-15</sup></td><td>212.8</td><td>S0/E</td><td>10.6</td><td>2.6 &times; 10<sup>40</sup></td><td>0.56</td><td>0.40</td></tr><tr><td>2CXO J000619.5-413019</td><td>1.5814</td><td>-41.5054</td><td>0.4</td><td>2.3 &times; 10<sup>-14</sup></td><td>19.5</td><td>S</td><td>1.9</td><td>1.1 &times; 10<sup>39</sup></td><td>0.58</td><td>0.00</td></tr><tr><td>2CXO J000620.2-413005</td><td>1.5842</td><td>-41.5016</td><td>0.4</td><td>8.9 &times; 10<sup>-14</sup></td><td>19.5</td><td>S</td><td>0.7</td><td>4.0 &times; 10<sup>39</sup></td><td>0.44</td><td>0.00</td></tr><tr><td>2CXO J000952.9+255547</td><td>2.4708</td><td>25.9299</td><td>0.5</td><td>4.4 &times; 10<sup>-15</sup></td><td>65.8</td><td>S</td><td>7.1</td><td>2.3 &times; 10<sup>39</sup></td><td></td><td></td></tr><tr><td>2CXO J000953.2+255454</td><td>2.4720</td><td>25.9153</td><td>0.5</td><td>2.1 &times; 10<sup>-15</sup></td><td>65.8</td><td>S</td><td>9.5</td><td>1.1 &times; 10<sup>39</sup></td><td>0.83</td><td>0.29</td></tr><tr><td>2CXO J000955.1+255536</td><td>2.4800</td><td>25.9267</td><td>0.7</td><td>2.5 &times; 10<sup>-15</sup></td><td>65.8</td><td>S</td><td>8.1</td><td>1.3 &times; 10<sup>39</sup></td><td>0.75</td><td>0.32</td></tr><tr><td>2CXO J001106.9-120631</td><td>2.7788</td><td>-12.1088</td><td>0.4</td><td>8.7 &times; 10<sup>-15</sup></td><td>83.3</td><td>S</td><td>2.2</td><td>7.2 &times; 10<sup>39</sup></td><td>0.25</td><td>0.09</td></tr><tr><td>2CXO J001815.4+300343</td><td>4.5646</td><td>30.0620</td><td>0.7</td><td>1.9 &times; 10<sup>-15</sup></td><td>93.9</td><td>S0/E</td><td>4.3</td><td>2.0 &times; 10<sup>39</sup></td><td>0.59</td><td>0.13</td></tr><tr><td>2CXO J001827.1+300210</td><td>4.6131</td><td>30.0363</td><td>0.5</td><td>6.7 &times; 10<sup>-15</sup></td><td>106.7</td><td>S</td><td>11.1</td><td>9.1 &times; 10<sup>39</sup></td><td>0.63</td><td>0.34</td></tr><tr><td>2CXO J001849.8-102134</td><td>4.7077</td><td>-10.3596</td><td>0.4</td><td>9.7 &times; 10<sup>-15</sup></td><td>116.4</td><td>S</td><td>4.5</td><td>1.6 &times; 10<sup>40</sup></td><td>0.43</td><td>0.28</td></tr><tr><td>2CXO J001850.4-102228</td><td>4.7102</td><td>-10.3746</td><td>0.4</td><td>4.8 &times; 10<sup>-15</sup></td><td>119.7</td><td>S</td><td>5.7</td><td>8.2 &times; 10<sup>39</sup></td><td>0.58</td><td>0.05</td></tr><tr><td>2CXO J001850.9-102232</td><td>4.7122</td><td>-10.3757</td><td>0.5</td><td>1.1 &times; 10<sup>-14</sup></td><td>119.7</td><td>S</td><td>2.2</td><td>1.8 &times; 10<sup>40</sup></td><td>0.57</td><td>0.01</td></tr><tr><td>2CXO J001850.9-102249</td><td>4.7125</td><td>-10.3804</td><td>0.5</td><td>1.8 &times; 10<sup>-15</sup></td><td>119.7</td><td>S</td><td>7.1</td><td>3.0 &times; 10<sup>39</sup></td><td>0.76</td><td>0.12</td></tr><tr><td>2CXO J001851.2-102244</td><td>4.7134</td><td>-10.3791</td><td>0.4</td><td>7.5 &times; 10<sup>-15</sup></td><td>119.7</td><td>S</td><td>5.1</td><td>1.3 &times; 10<sup>40</sup></td><td>0.56</td><td>0.05</td></tr><tr><td>2CXO J002751.6-014813</td><td>6.9653</td><td>-1.8037</td><td>2.7</td><td>1.4 &times; 10<sup>-13</sup></td><td>57.6</td><td>S</td><td>6.9</td><td>5.4 &times; 10<sup>40</sup></td><td>0.30</td><td>0.24</td></tr><tr><td>2CXO J003358.1-094222</td><td>8.4922</td><td>-9.7062</td><td>0.5</td><td>1.2 &times; 10<sup>-14</sup></td><td>52.9</td><td>S</td><td>17.2</td><td>4.2 &times; 10<sup>39</sup></td><td>0.75</td><td>0.54</td></tr><tr><td>2CXO J003404.3-094248</td><td>8.5182</td><td>-9.7133</td><td>0.5</td><td>1.1 &times; 10<sup>-14</sup></td><td>52.9</td><td>S</td><td>9.3</td><td>3.7 &times; 10<sup>39</sup></td><td>0.79</td><td>0.35</td></tr><tr><td>2CXO J003404.5-094239</td><td>8.5191</td><td>-9.7110</td><td>0.6</td><td>7.8 &times; 10<sup>-15</sup></td><td>52.9</td><td>S</td><td>8.4</td><td>2.6 &times; 10<sup>39</sup></td><td>0.41</td><td>0.24</td></tr><tr><td>2CXO J003408.4-094140</td><td>8.5351</td><td>-9.6947</td><td>1.2</td><td>1.3 &times; 10<sup>-14</sup></td><td>67.8</td><td>S</td><td>2.6</td><td>7.1 &times; 10<sup>39</sup></td><td>0.29</td><td>0.02</td></tr><tr><td>2CXO J003413.6-212803</td><td>8.5568</td><td>-21.4676</td><td>0.7</td><td>1.5 &times; 10<sup>-15</sup></td><td>96.3</td><td>S</td><td>4.7</td><td>1.7 &times; 10<sup>39</sup></td><td>0.61</td><td>0.09</td></tr><tr><td>2CXO J003414.9-212455</td><td>8.5622</td><td>-21.4155</td><td>0.5</td><td>1.8 &times; 10<sup>-15</sup></td><td>270.4</td><td>S0/E</td><td>12.6</td><td>1.6 &times; 10<sup>40</sup></td><td>0.84</td><td>0.18</td></tr><tr><td>2CXO J003416.0-212517</td><td>8.5669</td><td>-21.4215</td><td>0.4</td><td>2.7 &times; 10<sup>-15</sup></td><td>270.4</td><td>S0/E</td><td>18.9</td><td>2.4 &times; 10<sup>40</sup></td><td>0.60</td><td>0.46</td></tr><tr><td>2CXO J003654.5-010737</td><td>9.2271</td><td>-1.1271</td><td>1.1</td><td>1.4 &times; 10<sup>-15</sup></td><td>326.6</td><td>S</td><td>9.8</td><td>1.7 &times; 10<sup>40</sup></td><td>0.26</td><td>0.23</td></tr><tr><td>2CXO J003703.9-010904</td><td>9.2665</td><td>-1.1514</td><td>0.4</td><td>1.0 &times; 10<sup>-14</sup></td><td>328.1</td><td>S0/E</td><td>5.2</td><td>1.3 &times; 10<sup>41</sup></td><td>0.24</td><td>0.07</td></tr><tr><td>2CXO J003737.5-334255</td><td>9.4067</td><td>-33.7153</td><td>0.4</td><td>6.3 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>25.5</td><td>1.2 &times; 10<sup>40</sup></td><td></td><td></td></tr><tr><td>2CXO J003738.1-334306</td><td>9.4088</td><td>-33.7183</td><td>0.4</td><td>9.0 &times; 10<sup>-16</sup></td><td>126.5</td><td>S</td><td>22.2</td><td>1.7 &times; 10<sup>39</sup></td><td>0.67</td><td>0.15</td></tr><tr><td>2CXO J003738.3-334309</td><td>9.4098</td><td>-33.7192</td><td>0.4</td><td>1.0 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>20.8</td><td>1.9 &times; 10<sup>39</sup></td><td>0.61</td><td>0.13</td></tr><tr><td>2CXO J003738.7-334316</td><td>9.4114</td><td>-33.7212</td><td>0.4</td><td>7.5 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>20.0</td><td>1.4 &times; 10<sup>40</sup></td><td>0.37</td><td>0.13</td></tr><tr><td>2CXO J003739.1-334229</td><td>9.4131</td><td>-33.7083</td><td>0.4</td><td>2.9 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>22.0</td><td>5.6 &times; 10<sup>39</sup></td><td>0.75</td><td>0.13</td></tr><tr><td>2CXO J003739.2-334250</td><td>9.4134</td><td>-33.7139</td><td>0.4</td><td>4.4 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>14.6</td><td>8.5 &times; 10<sup>39</sup></td><td>0.83</td><td>0.06</td></tr><tr><td>2CXO J003739.3-334323</td><td>9.4141</td><td>-33.7231</td><td>0.4</td><td>2.6 &times; 10<sup>-14</sup></td><td>126.5</td><td>S</td><td>18.9</td><td>5.0 &times; 10<sup>40</sup></td><td>0.38</td><td>0.11</td></tr><tr><td>2CXO J003740.2-334327</td><td>9.4177</td><td>-33.7242</td><td>0.4</td><td>1.5 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>17.6</td><td>2.9 &times; 10<sup>39</sup></td><td>0.32</td><td>0.10</td></tr><tr><td>2CXO J003740.4-334324</td><td>9.4185</td><td>-33.7236</td><td>0.4</td><td>1.0 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>15.9</td><td>2.0 &times; 10<sup>39</sup></td><td>0.66</td><td>0.08</td></tr><tr><td>2CXO J003740.7-334258</td><td>9.4198</td><td>-33.7161</td><td>0.4</td><td>5.3 &times; 10<sup>-16</sup></td><td>126.5</td><td>S</td><td>2.7</td><td>1.0 &times; 10<sup>39</sup></td><td>0.53</td><td>0.00</td></tr><tr><td>2CXO J003740.8-334331</td><td>9.4203</td><td>-33.7253</td><td>0.4</td><td>4.1 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>18.8</td><td>7.8 &times; 10<sup>39</sup></td><td>0.56</td><td>0.11</td></tr><tr><td>2CXO J003741.2-334232</td><td>9.4218</td><td>-33.7090</td><td>0.4</td><td>1.3 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>15.4</td><td>2.6 &times; 10<sup>39</sup></td><td>0.83</td><td>0.07</td></tr><tr><td>2CXO J003741.3-334331</td><td>9.4223</td><td>-33.7254</td><td>0.4</td><td>8.9 &times; 10<sup>-16</sup></td><td>126.5</td><td>S</td><td>19.0</td><td>1.7 &times; 10<sup>39</sup></td><td>0.68</td><td>0.11</td></tr><tr><td>2CXO J003742.4-334249</td><td>9.4267</td><td>-33.7138</td><td>0.4</td><td>3.7 &times; 10<sup>-15</sup></td><td>126.5</td><td>S</td><td>10.8</td><td>7.1 &times; 10<sup>39</sup></td><td>0.70</td><td>0.04</td></tr><tr><td>2CXO J003742.4-334304</td><td>9.4270</td><td>-33.7178</td><td>0.4</td><td>9.1 &times; 10<sup>-16</sup></td><td>126.5</td><td>S</td><td>10.4</td><td>1.7 &times; 10<sup>39</sup></td><td>0.81</td><td>0.03</td></tr><tr><td>2CXO J003742.7-334212</td><td>9.4283</td><td>-33.7035</td><td>0.4</td><td>1.1 &times; 10<sup>-15</sup></td><td>128.2</td><td>S</td><td>6.7</td><td>2.3 &times; 10<sup>39</sup></td><td>0.87</td><td>0.03</td></tr><tr><td>2CXO J003742.8-334314</td><td>9.4286</td><td>-33.7207</td><td>0.4</td><td>8.7 &times; 10<sup>-16</sup></td><td>126.5</td><td>S</td><td>15.6</td><td>1.7 &times; 10<sup>39</sup></td><td>0.80</td><td>0.07</td></tr><tr><td>2CXO J003742.9-334204</td><td>9.4289</td><td>-33.7012</td><td>0.4</td><td>2.4 &times; 10<sup>-15</sup></td><td>128.2</td><td>S</td><td>4.7</td><td>4.8 &times; 10<sup>39</sup></td><td>0.63</td><td>0.01</td></tr><tr><td>2CXO J003743.8-334209</td><td>9.4327</td><td>-33.7028</td><td>0.4</td><td>2.4 &times; 10<sup>-15</sup></td><td>128.2</td><td>S</td><td>3.0</td><td>4.7 &times; 10<sup>39</sup></td><td>0.69</td><td>0.01</td></tr><tr><td>2CXO J003745.3-334228</td><td>9.4388</td><td>-33.7079</td><td>0.4</td><td>2.2 &times; 10<sup>-15</sup></td><td>155.4</td><td>S0/E</td><td>6.3</td><td>6.3 &times; 10<sup>39</sup></td><td>0.82</td><td>0.20</td></tr><tr><td>2CXO J003747.0-333953</td><td>9.4459</td><td>-33.6647</td><td>0.5</td><td>1.8 &times; 10<sup>-15</sup></td><td>127.9</td><td>S</td><td>5.5</td><td>3.6 &times; 10<sup>39</sup></td><td>0.70</td><td>0.07</td></tr><tr><td>2CXO J003912.0+005153</td><td>9.8000</td><td>0.8650</td><td>1.2</td><td>2.7 &times; 10<sup>-15</sup></td><td>59.7</td><td>S</td><td>5.9</td><td>1.1 &times; 10<sup>39</sup></td><td>0.74</td><td>0.31</td></tr><tr><td>2CXO J003913.2+005142</td><td>9.8051</td><td>0.8617</td><td>0.5</td><td>2.9 &times; 10<sup>-14</sup></td><td>59.7</td><td>S</td><td>2.6</td><td>1.2 &times; 10<sup>40</sup></td><td>0.68</td><td>0.03</td></tr><tr><td>2CXO J003917.1+031940</td><td>9.8214</td><td>3.3279</td><td>0.4</td><td>3.4 &times; 10<sup>-15</sup></td><td>61.6</td><td>S0/E</td><td>7.2</td><td>1.5 &times; 10<sup>39</sup></td><td>0.70</td><td>0.10</td></tr><tr><td>2CXO J003919.7+031945</td><td>9.8324</td><td>3.3294</td><td>0.4</td><td>4.2 &times; 10<sup>-15</sup></td><td>61.6</td><td>S0/E</td><td>5.6</td><td>1.9 &times; 10<sup>39</sup></td><td>0.83</td><td>0.10</td></tr></tbody></table>

**Notes.** Column (1): name of the source. (2–4): source coordinates and position error. (5): broad-band mean X-ray flux. (6): galaxy distance. (7): galaxy morphology. (8): physical separation of the source to the galaxy centre. (9): broad-band mean X-ray luminosity. (10): probability that the source is an XRB, given by the classifier. (11) fraction of ULX candidates being background contaminants within the separation of the ULX, given by the log N − log S method.