J/ApJ/944/1 DESI observations of the Andromeda galaxy (Dey+, 2023)
DESI observations of the Andromeda galaxy: revealing the immigration history of
our nearest neighbor.
Dey A., Najita J.R., Koposov S.E., Josephy-Zack J., Maxemin G., Bell E.F.,
Poppett C., Patel E., Beraldo Silva L. e, Raichoor A., Schlegel D.,
Lang D., Meisner A., Myers A.D., Aguilar J., Ahlen S., Allende Prieto C.,
Brooks D., Cooper A.P., Dawson K.S., de la Macorra A., Doel P.,
Font-Ribera A., Garcia-Bellido J., Gontcho Gontcho S. A, Guy J.,
Honscheid K., Kehoe R., Kisner T., Kremin A., Landriau M., Le Guillou L.,
Levi M.E., Li T.S., Martini P., Miquel R., Moustakas J., Nie J.,
Palanque-Delabrouille N., Prada F., Schlafly E.F., Sharples R.M.,
Tarle G., Ting Y.-S., Tyas L., Valluri M., Wechsler R.H., Zou H.
<Astrophys. J., 944, 1 (2023)>
=2023ApJ...944....1D 2023ApJ...944....1D
ADC_Keywords: Galaxies, nearby; Spectra, optical; Photometry, ugriz;
Abundances, [Fe/H]; Redshifts; Radial velocities;
H II regions; Planetary nebulae; QSOs
Keywords: Andromeda Galaxy ; Galaxy mergers ; Galaxy evolution ;
Galaxy dynamics ; Stellar kinematics ; Redshift surveys ;
Radial velocity ; Astrographic catalogs ; Catalogs
Abstract:
We present Dark Energy Spectroscopic Instrument (DESI) observations of
the inner halo of M31, which reveal the kinematics of a recent
merger-a galactic immigration event-in exquisite detail. Of the
11416 sources studied in 3.75hr of on-sky exposure time, 7438 are M31
sources with well-measured radial velocities. The observations reveal
intricate coherent kinematic structure in the positions and velocities
of individual stars: streams, wedges, and chevrons. While hints of
coherent structures have been previously detected in M31, this is the
first time they have been seen with such detail and clarity in a
galaxy beyond the Milky Way. We find clear kinematic evidence for
shell structures in the Giant Stellar Stream, the Northeast Shelf, and
Western Shelf regions. The kinematics are remarkably similar to the
predictions of dynamical models constructed to explain the spatial
morphology of the inner halo. The results are consistent with the
interpretation that much of the substructure in the inner halo of M31
is produced by a single galactic immigration event 1-2Gyr ago.
Significant numbers of metal-rich stars ([Fe/H]>-0.5) are present in
all of the detected substructures, suggesting that the immigrating
galaxy had an extended star formation history. We also investigate the
ability of the shells and Giant Stellar Stream to constrain the
gravitational potential of M31, and estimate the mass within a
projected radius of 125kpc to be
log10MNFW(<125kpc)/M☉=11.80-0.10+0.12. The results
herald a new era in our ability to study stars on a galactic scale and
the immigration histories of galaxies.
Description:
The Dark Energy Spectroscopic Instrument (DESI) is a wide-field,
fiber-fed multiobject spectroscopic instrument mounted on the Mayall
4m Telescope of the Kitt Peak National Observatory. Briefly, the ∼1.5"
diameter DESI fibers feed 10 three-arm spectrographs, which provide
continuous coverage over the wide wavelength range 3600-9800Å with
a resolving power R varying from ∼2000 in the blue to 5500 in the red.
DESI observations of M31 were obtained in 2021 January (TILEIDs 80713
and 80715, covering the optical disk of the galaxy) and 2022 January
(TILEID 82634, positioned on the Giant Stellar Stream; and 82635,
targeting the Northeast Shelf). In summary, DESI observed a total of
three tiles with a total effective exposure time of ∼3.75hr. The tiles
82634 and 82635 were each observed for an effective time of ∼1.5hr.
The DESI observations resulted in spectra of 11,554 unique
astronomical targets. Of these, 683 are confirmed as galaxies, and 184
as QSOs (see Appendix A).
The measured velocities and positions of the 6436 confirmed M31
stellar sources are presented in Table 2. The list of
spectroscopically confirmed star cluster, HII region, and planetary
nebula candidates is presented in Table 3. See Section 3.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
00 42 44.33 +41 16 07.5 M31 = NAME Andromeda Galaxy
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 122 7348 M31 stars
table3.dat 91 179 M31 HII, PNe, and GC targets
table6.dat 78 184 QSOs behind M31; see Appdendix A
table7.dat 72 684 Galaxies behind M31; see Appdendix A
mcat.dat 447 11361 DESI M31 measurement catalog
(DESIM31MEASUREMENT_CATALOG.fits);
see Appendix C
--------------------------------------------------------------------------------
Description of file:
DESIM31MEASUREMENT_CATALOG.fits is the original catalog in FITS
format as downloaded at DOI:10.5281/zenodo.6977494; see Appendix C.
See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
II/363 : The band-merged unWISE Catalog (Schlafly+, 2019)
II/365 : The CatWISE2020 cat. (updated version 28-Jan-2021) (Marocco+, 2021)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
VII/292 : DESI Legacy Imaging Surveys DR8 photometric redshifts (Duncan, 2022)
J/MNRAS/369/120 : Kinematic survey of planetary nebulae in M31 (Merrett+, 2006)
J/A+A/471/127 : Revised Bologna Catalog of M31 clusters, V.3 Galleti+, 2007)
J/ApJ/736/146 : Radial velocities of stars in Bootes I (Koposov+, 2011)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/758/133 : Metallicity profile of M31 HII regions & PNe (Sanders+, 2012)
J/ApJ/749/77 : MW halo. III. Statistical abundances (Schlaufman+, 2012)
J/ApJ/776/80 : PAndAS view of Andromeda satellites. I. (Martin+, 2013)
J/AJ/145/159 : LAMOST. II. ugriz photometry of 526 new quasars (Huo+, 2013)
J/other/RAA/15.1392 : LAMOST globular clusters in M 31 and M 33 (Chen+, 2015)
J/other/RAA/15.1438 : LAMOST new QSOs in M31 and M33 vicinity (Huo+, 2015)
J/ApJ/824/42 : Star clusters in M31. VII. GCl RVs (Caldwell+, 2016)
J/ApJ/833/167 : PAndAS view of Andromeda satellites. II. (Martin+, 2016)
J/AJ/152/45 : LAMOST survey of star clusters in M31. II. (Chen+, 2016)
J/ApJ/868/55 : Large-scale structure of M31 halo. II. (McConnachie+, 2018)
J/ApJ/883/128 : alpha & Fe in the giant stellar stream (Gilbert+, 2019)
J/ApJ/889/177 : RGB abund. in the disk, stream & halo of M31 (Escala+, 2020)
J/ApJ/902/51 : Abundances for M31 RGB stars from Keck/DEIMOS (Escala+, 2020)
J/ApJS/247/47 : UV survey of M31 with UVIT on AstroSat (Leahy+, 2020)
J/AJ/159/46 : Abundances of 416 stars in 5 dSphs of M31 (Kirby+, 2020)
J/A+A/645/A115 : 346 M31 star clusters and their parameters (Wang+, 2021)
J/A+A/658/A51 : New M31 star cluster candidates (Wang+, 2022)
J/AJ/164/20 : RGB RVs in M31 northeast shelf fields (Escala+, 2022)
J/other/Nat/603.599 : 247014 subgiant stars data (Xiang+, 2022)
http://www.desi.lbl.gov/ : DESI homepage
http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/community/pandas/csky.html :
PAndAS online data release
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- ID [1/7348] Internal running index identifier
6- 15 F10.7 deg RAdeg [8/14] Right Ascension (J2000)
17- 26 F10.7 deg DEdeg [37/44] Declination (J2000)
28- 33 F6.1 km/s Vlos [-639/270] Line of sight heliocentric velocity
35- 39 F5.1 km/s e_Vlos [0/150] Uncertainty in Vlos
41- 45 F5.2 [Sun] [Fe/H] [-4/1] Spectroscopic estimate of [Fe/H]
47- 50 F4.2 [Sun] e_[Fe/H] [0/5.6]? Uncertainty in [Fe/H]
52- 58 F7.1 K Teff [2300/13755] Effective temperature
60- 65 F6.1 K e_Teff [0.2/4119]? Uncertainty in Teff
67- 71 F5.2 [cm/s2] logg [-0.5/6] log surface gravity
73- 76 F4.2 [cm/s2] e_logg [0/4] Uncertainty in log(g)
78- 82 F5.2 mag Gmag [11/21.6]? Gaia DR2 G band apparent magnitude
84- 88 F5.2 mag gmag [17.38/27.33]? PAndAS g-band apparent magnitude
90- 94 F5.2 mag imag [16.86/22.8]? PAndAS i-band apparent magnitude
96-122 A27 --- AName Alternate target name from Gaia DR2 or PAndAS
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- ID [1/179] Internal running index identifier
6- 15 F10.7 deg RAdeg [8.9/13.5] Right Ascension (J2000)
17- 26 F10.7 deg DEdeg [39.9/42.6] Declination (J2000)
28- 33 F6.1 km/s Vlos [-713/54] Line of sight heliocentric velocity
35- 38 F4.1 km/s e_Vlos [0/17] Uncertainty in Vlos
40- 46 A7 --- Class Target class (1)
48- 52 F5.2 mag Gmag [15.99/22]? Gaia DR2 G band apparent magnitude
54- 58 F5.2 mag gmag [16/22.8]? PAndAS g-band apparent magnitude
60- 64 F5.2 mag imag [15.2/35]? PAndAS i-band apparent magnitude
66- 91 A26 --- AName Alternate target name (2)
--------------------------------------------------------------------------------
Note (1): The reason the source was targeted, i.e., whether it was a potential
emission line ("H2PN") or star cluster ("cluster") candidate.
Note (2): From Sanders+ (2012, J/ApJ/758/133; <[SCM2012b] HIINNN>,
<[SCM2012b] PNhNNN> or <[SCM2012b] PNNNN> in Simbad);
Galleti+ (2007, J/A+A/471/127 & 2014, see V/143;
<M31GC JHHMMSS+DDMMSS> in Simbad).
"GC" stands for "Galactic Cluster" candidate and does not
distinguish between young and old clusters.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- ID [1/184] Internal running index identifier
6- 15 F10.7 deg RAdeg [8/14] Right Ascension (J2000)
17- 26 F10.7 deg DEdeg [37/44] Declination (J2000)
28- 32 F5.3 --- z [0.09/3.5] Spectroscopic redshift
34- 38 F5.2 mag Gmag [17.68/21.1]? Gaia DR2 G band apparent magnitude
40- 44 F5.2 mag gmag [17.7/24.25]? PAndAS g-band apparent magnitude
46- 50 F5.2 mag imag [17.64/34.8]? PAndAS i-band apparent magnitude
52- 59 A8 --- --- [Gaia DR3]
61- 78 I18 --- GaiaDR3 ? The Gaia DR3 identifier
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- ID [1/684] Internal running index identifier
6- 15 F10.7 deg RAdeg [8.3/14] Right Ascension in decimal degrees (J2000)
17- 26 F10.7 deg DEdeg [37/44] Declination in decimal degrees (J2000)
28- 32 F5.3 --- z [0.03/1.6] Spectroscopic redshift
34- 38 F5.2 mag gmag [18.34/27.34]? PAndAS g-band apparent magnitude
40- 44 F5.2 mag imag [17/22.81]? PAndAS i-band apparent magnitude
46- 72 A27 --- AName Alternate name, where available
--------------------------------------------------------------------------------
Byte-by-byte Description of file: mcat.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- targetID DESI target identification (TARGETID)
21- 37 I17 --- Dup DESI targetID of the duplicate entry for
this source if one exists; 0 otherwise
(DUPLICATE)
39 I1 --- Prim 1=Primary entry; O=otherwise; only for
duplicate entries (PRIMARY)
41- 51 F11.7 deg RAdeg [8/14] Right ascension (J2000) (RA)
53- 63 F11.7 deg DEdeg [37/44] Declination (J2000) (DEC)
65- 75 F11.3 km/s HRVBest [-713/1037934] "Best" heliocentric radial
velocity (VRAD_BEST)
77- 83 F7.3 km/s e_HRVBest [0.02/187] HRVBest uncertainty
(VRADBESTERR)
85- 93 F9.3 km/s HRV [-1500/1500] Heliocentric radial velocity
(VRAD)
95- 102 F8.3 km/s e_HRV [0.02/1865] HRV uncertainty (VRAD_ERR)
104- 110 F7.3 km/s Skew [-85/33] Skew on the heliocentric radial
velocity from DESI's RV Pipeline (VRAD_SKEW)
112- 119 F8.3 km/s Kurt [1/8567] Kurtosis on the heliocentric
radial velocity from DESI's RV Pipeline
(VRAD_KURT)
121- 127 F7.4 [cm/s2] logg [-0.51/6] Log of surface gravity (LOGG)
129- 135 F7.1 K Teff [2300/15000] Effective temperature (TEFF)
137- 143 F7.4 [-] [Fe/H] [-4/1] Metallicity (FEH)
145- 151 F7.5 [cm/s2] e_logg [0.0001/4] logg uncertainty (LOGG_ERR)
153- 159 F7.2 K e_Teff [0.16/4119]? Teff uncertainty (TEFF_ERR)
161- 167 F7.5 [-] e_[Fe/H] [0.00013/6]? [Fe/H] Uncertainty (FEH_ERR)
169 I1 --- f_RVS [0/7] Warning flags for the RVS pipeline
reductions (0=good) (RVS_WARN)
171- 198 A28 --- Class Selection class(es) for the target (CLASS)
200- 259 A60 --- AName Alternate designation of the target
(DESIGNATION)
261- 278 I18 --- GaiaDR3 ?=-9 Gaia DR3 unique identification number
(GDR3_ID)
280- 285 A6 --- spType Spectroscopic type: STAR, GALAXY or QSO
(SPECTYPE)
287- 303 A17 --- TILEID DESI Tiles contributing to the spectrum
(TILEID)
305- 315 F11.6 --- SNB [-1.1/241] Signal-to-noise ratio in the
blue arm of the DESI spectrograph (SN_B)
317- 327 F11.6 --- SNR [-0.9/339] Signal-to-noise ratio in the red
arm of the DESI spectrograph (SN_R)
329- 338 F10.6 --- SNZ [0/411] Signal-to-noise ratio in the NIR
arm of the DESI spectrograph (SN_Z)
340- 350 F11.3 km/s HRVRed [-600/1037934] Heliocentric radial velocity
from the DESI Redrock pipeline
(VRAD_REDROCK)
352- 358 F7.3 km/s e_HRVRed [0.04/187] HRVRed uncertainty
(VRADREDROCKERR)
360- 363 I4 --- f_HRVRed [0/1056] Warning flags for Redrock pipeline
reductions (0=good) (REDROCK_ZWARN)
365- 375 F11.3 km/s HRVvi [-10000/1037974] Heliocentric radial
velocity from the Visual Inspection
(VRAD_VI)
377- 378 I2 --- q_HRVvi [-9/4] Quality flag from the Visual
Inspection (≥3 is good; ≤2 is bad; <0 is
not
inspected) (VI_QUALITY)
380- 385 A6 --- spTypeVI Spectral type from the Visual Inspection
("STAR", "GALAXY" or "QSO"; blank if
unknown) (VI_SPECTYPE)
387- 391 F5.3 deg Dist [0.02/4.2] Projected radial distance from
the center of M31 (M31DIST)
393- 399 F7.4 mag Gmag [0/22]? Gaia DR3 G-band magnitude (GAIA_G)
401- 407 F7.4 mag gmag [16/35.5]?=0 PAndAS g-band magnitude
(PANDAS_G)
409- 415 F7.4 mag imag [15.2/35]?=0 PAndAS i-band magnitude
(PANDAS_I)
417- 425 F9.6 mag zmag [0.07/21.6]?=0 Predicted Legacy Surveys
z-band AB magnitude (PRED_Z)
427- 432 F6.3 deg xi [-2/2.4] Standard ξ coordinate in frame
centered on M31 (XI)
434- 439 F6.3 deg eta [-4.2/2.5] Standard η coordinate in
frame centered on M31 (ETA)
441- 447 F7.3 deg theta Polar angle centered on M31 and measured
clockwise from the west
(as in Figures 6, 7, 11, and 12) (THETA)
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History:
From electronic version of the journal for tables 2, 3, 6 and 7
DESIM31MEASUREMENT_CATALOG.fits downloaded at:
http://zenodo.org/records/6977494 (DOI:10.5281/zenodo.6977494)
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 16-Jan-2025