銀河進化研究会2017@大阪
2017年6月7-9日

MOIRCS Upgrade Project: A NIR Redshift Survey of the Cluster RXJ1716 at z=0.8
Ichi Tanaka*1, Yusei Koyama*1, Maximilian Fabricius*1,2, Josh Walawender*1,3, Tadayuki Kodama*4, Ikuru Iwata*1, and Nobuo Arimoto*1*1) Subaru Telescope, NAOJ *2) MPE 3) Keck Telescope, 4) NAOJ

MOIRCS is Subaru’s Near Infrared Camera and MOS Spectrograph. We have upgraded the detector from the old Hawaii2 to Hawaii2 RG in late 2015. Through the series of Engineeringobservations in 2016, we have shown that the overall on-sky performance has improved much, especially in the shorter wavelength.
As a part of the science verification test, we took the J-band spectra of the star-forming galaxies in the rich X-ray cluster RX J1716+6416 at z=0.81 in MOS mode. Koyama et al. (2010
MNRAS, 391, 1758) has investigated the environmental dependence of the star-formation activity using the sample of the Hα emitters (HAEs) detected through the deep and wide
MOIRCS Narrowband (NB) imaging as well as the multiwavelength data. As the spectroscopic follow-up of their detected HAEs, we tried to measure the redshift of their HAE sample forthe cluster kinematics. By using the zJ500 grism + J imaging filter, we can cut well over 100 target slits in a single MOS mask. We have successfully measured the redshift of 42 objects(including all the 31 HAEs) in only 45-minutes exposure under less good condition (EL~30 degrees, seeing ~0.8”). This makes more than double the number of objects with measured
redshifts from Gioia et al.(1999). With the unpublished FOCAS spectroscopic data provided by YK, the kinematical properties of the cluster is examined. We have shown that, as inferredfrom the previous analysis by Koyama+2011, there is a clear substructure kinematically distinct from the main cluster. Interestingly, the fraction of the HAEs in the structure show thegradual decline towards the direction of the main cluster, despite that there is no clear concentration of galaxies. The suppression of the star-formation before the direct interaction withmain cluster may already be on work. Behind the contact front, there is the area with the unusually high HAE fraction which we newly found from the data. Our result nicely
demonstrates the improved performance of the MOIRCS.

Koyama etal.(2010)
Green Box = MOIRCS FOV
this time.

Red Circles = HAEs
Blue lines = Slit position

Channel 2Over 100 spectraat the same time!

111
Slits!

Spec. Total Efficiency

MOIRCS is Subaru’s Near Infrared Camera and
MOS Spectrograph. It has been working over 10years since its first light. In order to keep its
competitiveness, we started the MOIRCS Upgrade
Project since 2012. As the part of the project, wehave replaced the detector from the old Hawaii2 toHawaii2 RG in late 2015. We have shown that,through the series of Engineering observations in2016, the overall on-sky performance has improved
much, especially in the shorter wavelength.

The Data:
Observing Date: 2016-06-17 27:00-28:00
Total Exposure Time: 2700 sec (45 min.)
Data taken at the target EL~30 degrees,very slight cirrus, and the ~0.8” seeing.
Definitely Not a Great Condition!

Reduction

Channel 1

As a part of the science verification program, we haveexecuted the spectroscopy of the Hα Emitters (HAEs) in thecluster RX J1716+6416 at z=0.81 with MOS mode. The HAEs
sample were selected via the deep MOIRCS NB imaging by
Koyama et al. (2010). Though there are large number of HAEs
in the cluster, very small number of them were with spec-z.
Using a special layout of J+zJ500 grism, we can easily locate
over 100 slit at the same time (x3-4 of the usual setting) !

(Left) The measured distribution of
the emission line wavelengths of ourdata (red: ch1, blue: ch2) iscompared with the data by Gioia et al. (1999: grey). Blue and red bar show
slight difference of the distribution.
But overall they represent that ofGioia+99. The distribution is wellmatched to the NB transmission
window (see inset) for the HAE
selection.

The 2-D spectra. Emission-line detection is 42, 31 of which
are HAEs. 31 are the first-time z measurement (among
published data: YK actually has more).

* Yellow Star = the center of the cluster.

(Right) The size of bubble
represents
theredshift(large=close, small=far). The
red bubble represents theMOIRCS data, while blue
bubble represents the datafrom Gioia+99.

To see the significance of the dynamical substructure,
Dressler & Schectman (1986) employed the formula below
to express the significance of the substructure of acluster (δ: hereafter DS86 parameter).
Cluster Center(Right) 3-D view (cross view)
ofthecluster
galaxydistribution. In the figure,red, yellow, and blue marks
each represent the current
data, Gioia+99, and YK’s
unpublished FOCAS data.

In the left figure, the diameter of the bubble
represents the DS86 δ value. Orange circles are the datafrom this work., while the open circles are from Gioia+99
and our FOCAS data (by YK).
The kinematic properties of the area taken by MOIRCS(red) is strikingly different from the cluster center(yellow star), suggesting that the region observed thistime is a large subcluster.

(Right) The phase space diagram. The
substructure is not well recognized in the figure.
Red = quiescent galaxies from Gioia99,
Blue=MOIRCS HAEs, Green=Koyama+. Asterisks
are the Hα-brightest-7 HAEs. Distribution iswell within the area where the star-forming
cluster galaxies are typically seen (0.5 – 2
R/R200, +-1 from V/sigma=0.

The relation between the Stellar Mass and theStar-formation rate (Main Sequence). The
SFR from the NB filter data (blue: YK) andfrom the current spec data (orange: this work)
is compared (inset), finding no systematic bias.
Overall the two estimate agrees within
uncertainty. Yellow line is for the field value at
0.81 Speargel et al.(2014).

Zoom-up of the observed field. The white and red
circles each represents the photo-z selected and theHAE members. The green large circle represents theDS86 δ parameter (larger = more likely substructure).
The fraction of HAEs among the photo-z member andthe existence of the substructure is evident.

“Non-HAE fraction”: for each galaxy, the fraction of HAEs
among the adjacent 10 galaxies (include itself) is evaluated andis expressed in the color scale. The overlaid open circle indicatesthe DS86 δ parameter. Note that for field members the nonHAE fraction is typically 0.6-0.7. There are a pocket ofstunningly-high HAE fraction at the lower right area (arrow).

Mass-Metallicity Relation for RXJ 1716.
Background is for the field sample at z~0.8
from De Los Reyes et al.(2015). TheMetallicity is estimated by the N2 index.
Though the current shallow data is shallow andthe [NII] is only the upper limit for most of
the sample, we can expect a more detection by
a few hours’ observation.

Our (only) 45-minutes performance verification data effectively demonstrates the improved
performance of MOIRCS. We can measure the redshift of ALL the known HAEs, and can add
more than 30 new redshifts for the cluster. Some of them have the [NII] detection too,enabling us to measure metallicity. The analysis of the dynamical condition of the cluster has
revealed the presence of the sheet-like substructure at the south-west of the cluster
center. There we also find a “pocket” of the significantly-enhanced star-formation activity.
We will try to measure the metallicity by the N2 index in the future.
With the technique we demonstrated here, we can get the spectra for a few hundreds
objects per a night for the crowded region. We can study the dynamics, star-formation
activity, and even metallicity of the cluster at z~1 based on ~300 spec data in only a night.
MOIRCS is the ideal instrument for the follow-up studies of z~1 clusters discovered by theHSC SSP (e.g. Yamamoto et al. HSC-HSC; etc).