J/ApJ/830/14 SIGMA: Keck spectra of z~2 gal. in CANDELS fields (Simons+, 2016) ================================================================================ Kinematic downsizing at z ~ 2. Simons R.C., Kassin S.A., Trump J.R., Weiner B.J., Heckman T.M., Barro G., Koo D.C., Guo Y., Pacifici C., Koekemoer A., Stephens A.W. =2016ApJ...830...14S (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Galaxies, spectra ; Spectra, infrared ; Rotational velocities ; Redshifts ; Velocity dispersion ; Surveys Keywords: galaxies: evolution; galaxies: formation; galaxies: fundamental parameters; galaxies: kinematics and dynamics Abstract: We present results from a survey of the internal kinematics of 49 star-forming galaxies at z~2 in the CANDELS fields with the Keck/MOSFIRE spectrograph, Survey in the near-Infrared of Galaxies with Multiple position Angles (SIGMA). Kinematics (rotation velocity V_rot_ and gas velocity dispersion {sigma}_g_) are measured from nebular emission lines which trace the hot ionized gas surrounding star-forming regions. We find that by z~2, massive star-forming galaxies (logM_*_/M_{sun}_>~10.2) have assembled primitive disks: their kinematics are dominated by rotation, they are consistent with a marginally stable disk model, and they form a Tully-Fisher relation. These massive galaxies have values of V_rot_/{sigma}_g_ that are factors of 2-5 lower than local well-ordered galaxies at similar masses. Such results are consistent with findings by other studies. We find that low-mass galaxies (logM_*_/M_{sun}_<~10.2) at this epoch are still in the early stages of disk assembly: their kinematics are often dominated by gas velocity dispersion and they fall from the Tully-Fisher relation to significantly low values of V_rot_. This "kinematic downsizing" implies that the process(es) responsible for disrupting disks at z~2 have a stronger effect and/or are more active in low-mass systems. In conclusion, we find that the period of rapid stellar mass growth at z~2 is coincident with the nascent assembly of low-mass disks and the assembly and settling of high-mass disks. Description: The Survey in the near-Infrared of Galaxies with Multiple position Angles (SIGMA) sample is drawn from three of the fields (GOODS-S, GOODS-N and UDS) of the HST/WFC3 CANDELS survey (Grogin+ 2011ApJS..197...35G; Koekemoer+ 2011ApJS..197...36K). All of the spectra in GOODS-N were taken as a part of the TKRS-2 survey (Wirth+ 2015, J/AJ/150/153) and a subset of the spectra in GOODS-S and UDS have been presented in previous papers (Trump+ 2013ApJ...763L...6T; Barro+ 2014ApJ...795..145B). The properties of the full sample are presented in Table 1. The spectra in this sample were taken in the MOSFIRE H-band (1.46-1.81um) and K-band (1.93-2.45um) on Keck I (R~3630 in both bands). File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 57 49 SIGMA - Observational and physical properties table2.dat 56 49 SIGMA - Observational and kinematic properties -------------------------------------------------------------------------------- See also: J/AJ/150/153 : Team Keck Redshift Survey 2 (TKRS2) (Wirth+, 2015) J/A+A/582/A21 : Merging galaxies (mis)alignments (Barrera-Ballesteros+, 2015) J/AJ/149/178 : Redshift cat. of galaxies in GOODS-South field (Morris+, 2015) J/ApJS/207/24 : GOODS-S CANDELS multiwavelength catalog (Guo+, 2013) J/ApJS/206/10 : CANDELS multiwavelength catalog (Galametz+, 2013) J/ApJ/768/74 : PHIBSS: CO obs. of star-forming galaxies (Tacconi+, 2013) J/ApJS/203/24 : Structural param. of galaxies in CANDELS (van der Wel+, 2012) J/A+A/539/A91 : MASSIV I. Sample properties (Contini+, 2012) J/MNRAS/417/2347 : Tully-Fisher relation for SDSS galaxies (Reyes+, 2011) J/ApJ/741/115 : Deep spectroscopy in the GOODS fields (Miller+, 2011) J/A+A/533/A119 : GOODS-Herschel North and South catalogs (Elbaz+, 2011) J/MNRAS/401/2113 : GHASP: H{alpha} data cubes for 153 galaxies (Epinat+, 2010) J/ApJ/706/1364 : SINS survey of high-redshift gal. (Forster Schreiber+, 2009) J/ApJ/653/1027 : TKRS/GOODS-N Field galaxies (Weiner+, 2006) J/A+A/455/107 : 3D spectroscopy with VLT/GIRAFFE (Flores+, 2006) J/ApJ/633/844 : Stellar mass in disk-dominated galaxies (Pizagno+, 2005) J/A+A/430/115 : SFR of distant galaxies (Hammer+, 2005) Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 5 I5 --- ID [1826/26736] SIGMA galaxy ID 7- 8 I2 h RAh Hour of Right Ascension (J2000) (1) 10- 11 I2 min RAm Minute of Right Ascension (J2000) (1) 13- 17 F5.2 s RAs Second of Right Ascension (J2000) (1) 19- 19 A1 --- DE- Sign of the Declination (J2000)(1) 20- 21 I2 deg DEd Degree of Declination (J2000) (1) 23- 24 I2 arcmin DEm Arcminute of Declination (J2000) (1) 26- 30 F5.2 arcsec DEs Arcsecond of Declination (J2000) (1) 32- 35 F4.2 --- zsp [1.3/2.5] Spectroscopic redshift 37- 41 F5.2 mag Hmag [21.1/26.6] AB H band magnitude (2) 43- 47 F5.2 [Msun] Mstar [9.2/11.8] Stellar galaxy mass (3) 49- 52 F4.2 [Msun/yr] SFR [0.2/3.7] Star formation rate (3) 54- 57 F4.2 --- b/a Aspect ratio in the H band continuum (2) -------------------------------------------------------------------------------- Note (1): The galaxy ID, RA (J2000) and DEC (J2000) are matched with the publicly available CANDELS catalogs in Galametz+ (2013, J/ApJS/206/10); Guo+ (2013, J/ApJS/207/24) Note (2): Adopted from the GALFIT measurements on the HST/WFC3 F160W CANDELS image in van der Wel+ (2012, J/ApJS/203/24). Note (3): Derived from the full galaxy SED, as described in Section 3.2. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 5 I5 --- ID [1826/26736] SIGMA galaxy ID 7- 7 I1 --- Ns Number of spectra in the full SIGMA sample 9- 13 F5.1 deg PAphot [-87/89] H-band continuum photometric major axis 15- 18 F4.1 deg e_PAphot [0.2/22] Uncertainty in PAphot 20- 25 F6.1 deg PAslit [-297/121] Keck/MOSFIRE slit position angle, maximum vsini 27- 30 F4.1 deg DeltaPA [1.6/87.7] Difference between PAphot, PAslit 32- 34 F3.1 arcsec rv [0.1/0.4] Fixed turnover radius of the rotation curve model 36- 38 I3 km/s vsini [5/318] Projected rotational velocity, from the flat part of the best-fit rotation curve 40- 41 I2 km/s e_vsini [14/78] Uncertainty in vsini 43- 45 I3 km/s Vrot [5/448]? Inclination corrected rotational velocity 47- 49 I3 km/s e_Vrot [15/150]? Uncertainty in Vrot 51- 53 I3 km/s sigg [10/129] {sigma}g, best-fit gas velocity dispersion 55- 56 I2 km/s e_sigg [5/83] Uncertainty in {sigma}g -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Emmanuelle Perret [CDS] 16-Jan-2017