<figure><img src="image_1.png" /></figure>

Erratum: “FAST Reveals New Evidence for M94 as a Merger” (2023, ApJ, 952, 130)

Ruilei Zhou<sup>1,2,3</sup> (D), Ming Zhu<sup>1,2,3,4</sup> (D), Yanbin Yang<sup>5</sup> (D), Haiyang Yu<sup>1,2,3</sup> (D), Lixia Yuan<sup>6</sup> (D), Peng Jiang<sup>1,3,4</sup> (D), and Wenzhe Xi<sup>2,7</sup> (D)

<sup>1</sup> National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Beijing 100101, People's Republic of China; mz@nao.cas.cn

<sup>2</sup> University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China

<sup>3</sup> CAS Key Laboratory of FAST, National FAST, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, People's Republic of China

<sup>4</sup> Guizhou Radio Astronomical Observatory, Guizhou University, Guiyang 550000, People's Republic of China

<sup>5</sup> GEPI, Observatoire de Paris, CNRS, Place Jules Janssen 92195, Meudon, France

<sup>6</sup> Purple Mountain Observatory and Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 10 Yuanhua Road, Qixia District, Nanjing 210033, People's Republic of China

<sup>7</sup> Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011, People's Republic of China

Received 2024 January 21; published 2024 February 20

In the published article, we inadvertently made a mistake in the conversion from flux density to brightness temperature in Figure 4. Now we decide to show the flux density in the unit of Jy beam⁻¹ instead of brightness temperature for the three spectra in this figure. The position of the peak column density of Cloud 9 is also adjusted slightly.

We also found that the velocity range of Cloud 9 should be 270–319 km s⁻¹, instead of 290–319 km s⁻¹. The previous range covers the majority of the H I emission from Cloud 9, but missed some diffuse emission in the velocity range of 270–290 km s⁻¹. As a result, the total H I flux and H I mass for Cloud 9 should be modified slightly, but these changes do not affect the conclusion of the published article.

With the updated velocity range of Cloud 9, the σ of Cloud 9 in Figure 4 and the H I flux and $M_{H\i}$ of Cloud 9 should be $2.9 \times 10^{17} \text{cm}^{-2}$, $0.229 \pm 0.02 \text{Jy km s}^{-1}$, and $(11.7 \pm 1.0) \times 10^5 M_{\odot}$, respectively. Updated versions of Figure 1, Figure 4, and Table 1 are provided here.

The fourth sentence of the abstract becomes: “We measured a total integrated flux (including all clouds/filament) of 127.4 (±1) Jy km s⁻¹, corresponding to a H I mass of $(6.51 \pm 0.06) \times 10^8 M_{\odot}$, which is 63.1% more than that observed by THINGS.”

The fifth sentence of Section 3.1 becomes: “The FAST contour levels starting at $3\sigma$ ($2.5 \times 10^{18} \text{cm}^{-2}$ for the M94 region, and $8.6 \times 10^{17} \text{cm}^{-2}$ for the lower right subpanel) is much lower than that of the THINGS map, which is $1.3 \times 10^{20} \text{cm}^{-2}$.”

The first sentence of Section 3.2 becomes: “By integrating all the H I flux in Figure 1, including the H I structures discussed in the next section, we measured a total integrated flux of $127.4 (±1) \text{Jy km s}^{-1}$, or H I mass of $(6.51 \pm 0.06) \times 10^8 M_{\odot}$ for M94.”

The second sentence of the last paragraph in Section 3.3 becomes: “The FAST contour levels start at $3\sigma$ ($8.1 \times 10^{17}$, $6.8 \times 10^{17}$, and $8.6 \times 10^{17} \text{cm}^{-2}$ for high-velocity clouds (HVCs) 3 and 6, and Cloud 9, respectively) in steps of $3\sigma$.”

The last sentence of the first paragraph in Section 3.4 becomes: “They were masked at $3\sigma$ of column density ($2.5 \times 10^{18} \text{cm}^{-2}$ for the M94 region, and $8.6 \times 10^{17} \text{cm}^{-2}$ for the lower right subpanel) and a few obvious bad pixels were masked manually.”

The second sentence of the first paragraph in Section 4.2 should now read: “Its H I flux is $0.229 \pm 0.02 \text{Jy km s}^{-1}$, corresponding to a mass of $(11.7 \pm 1.0) \times 10^5 M_{\odot}$.”

The tenth and eleventh sentences of the third paragraph in Section 4.2 become: “Thus, the baryonic mass of Cloud 9 is about $1.56 \times 10^6 M_{\odot}$. The dynamical mass to total baryonic mass ratio is derived to be about 224, implying that dark matter absolutely dominates over baryons in Cloud 9.”

<figure><img src="image_2.png" /></figure>
<figure><img src="image_3.png" /><figcaption>**Figure 1.** Top: the H I integrated intensity map of M94 region with the THINGS and FAST contours overlaid on it. The blue contours are FAST data integrated over 114–504 km s⁻¹ and contour levels are 0.2, 0.7, 1.9, 4.4, 11.0, 21.0, 33.4, 45.8, and 58.3 × 10¹⁹ cm⁻². The green contours are THINGS images integrated over 144–490 km s⁻¹, and contour levels start at 1.3 × 10²⁰ cm⁻² and increment by 2.5 × 10²⁰ cm⁻². Bottom: the same FAST contours overlaid on a DESI-LS optical image. The lower right corner of both panels shows Cloud 9 integrated over 270–319 km s⁻¹ with contour levels starting at 8.6 × 10¹⁷ cm⁻² in steps of 8.6 × 10¹⁷ cm⁻². The numbers represent names of the H I features indicated by the corresponding arrows. The crosses stand for possible features of HVC 3 and 6.</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>**Figure 4.** Top: the FAST integrated flux density contours of the H I detected by FAST superimposed on the DESI-LS optical image for HVCs 3 and 6, and Cloud 9, respectively, and the integrated velocity range is from Table 1. The contour levels start at $3\sigma$ (8.1 $\times 10^{17}$, 6.8 $\times 10^{17}$, and 8.6 $\times 10^{17}$ cm$^{-2}$ for HVCs 3 and 6, and Cloud 9, respectively) in steps of $3\sigma$. FAST's HPBW is indicated in the bottom left corner. Bottom: spectra taken at the peak column density of HVCs 3 and 6, and Cloud 9. The vertical axis is flux density and the horizontal axis is velocity.</figcaption></figure>

<table><caption>**Table 1**

Properties of the H I Filament and Eight H I Structures</caption><thead><tr><th></th><th>R.A.<br>(hh:mm:ss)<br>(2)</th><th>Decl.<br>(dd:mm:ss)<br>(3)</th><th>Velocity Range<br>(km s<sup>-1</sup>)<br>(4)</th><th>Mean Velocity<br>(km s<sup>-1</sup>)<br>(5)</th><th>Diameter<br>(arcmin)<br>(6)</th><th>H I Flux<br>(Jy km s<sup>-1</sup>)<br>(7)</th><th>M<sub>H I</sub><br>(×10<sup>5</sup>M<sub>☉</sub>)<br>(8)</th></tr></thead><tbody><tr><td>1</td><td>12:51:42 ~ 12:53:12</td><td>+40:54:30 ~ +41:17:33</td><td>260-426</td><td>355</td><td>11, 26</td><td>5.646 ± 0.1</td><td>288.9 ± 5.0</td></tr><tr><td>2</td><td>12:51:52</td><td>+41:17:27</td><td>338-387</td><td>341</td><td>4</td><td>0.125 ± 0.005</td><td>6.4 ± 2.0</td></tr><tr><td>3</td><td>12:51:14</td><td>+41:35:28</td><td>226-260</td><td>248</td><td>4</td><td>0.100 ± 0.03</td><td>5.1 ± 1.0</td></tr><tr><td>4</td><td>12:50:24</td><td>+41:31:37</td><td>304-353</td><td>325</td><td>6</td><td>0.329 ± 0.003</td><td>16.8 ± 1.0</td></tr><tr><td>5</td><td>12:50:16</td><td>+41:19:22</td><td>231-314</td><td>292</td><td>8</td><td>0.714 ± 0.04</td><td>36.5 ± 2.0</td></tr><tr><td>6</td><td>12:48:35</td><td>+41:18:14</td><td>348-377</td><td>368</td><td>4</td><td>0.080 ± 0.04</td><td>4.1 ± 2.0</td></tr><tr><td>7</td><td>12:48:35</td><td>+41:09:12</td><td>245-294</td><td>285</td><td>8</td><td>0.683 ± 0.03</td><td>34.9 ± 2.0</td></tr><tr><td>8</td><td>12:51:20</td><td>+41:08:29</td><td>363-416</td><td>392</td><td>6</td><td>0.980 ± 0.1</td><td>50.1 ± 3.0</td></tr><tr><td>9</td><td>12:51:52</td><td>+40:17:29</td><td>270-319</td><td>298</td><td>6</td><td>0.229 ± 0.02</td><td>11.7 ± 1.0</td></tr></tbody></table>

**Note.** Columns (2) and (3): R.A. and decl. (J2000.0) are the right ascension and declination of the peak column density of each cloud, respectively, except H I filament, which is the position range. Column (4): velocity range is the range that the H I filament or clouds are visible. Column (5): mean velocity of H I structures. Column (6): diameter refers to the diameter of circles similar in size to clouds (major and minor axis, respectively, for an ellipse of H I filament 1). Column (7): H I flux is integrated within the extent of these ellipses and circles. Column (8): $M_{H I}$ is the H I mass of the cloud, in solar masses, calculated by $M_{H I}/M_{☉} = 2.356 \times 10^5 D^2 S$, where D is the distance to the object in Mpc and S is the H I flux.

ORCID iDs

Ruilei Zhou https://orcid.org/0009-0009-0581-5237

Ming Zhu https://orcid.org/0000-0001-6083-956X

Yanbin Yang https://orcid.org/0000-0001-7949-3407

Haiyang Yu https://orcid.org/0000-0001-9838-7159

Lixia Yuan https://orcid.org/0000-0003-0804-9055

Peng Jiang https://orcid.org/0000-0002-5387-7952

Wenzhe Xi https://orcid.org/0009-0000-7751-9458