J/ApJ/646/133 Redshifts in X-ray-selected groups of galaxies (Mulchaey+, 2006)
X-ray-selected intermediate-redshift groups of galaxies. Mulchaey J.S., Lubin L.M., Fassnacht C., Rosati P., Jeltema T.E. <Astrophys. J., 646, 133-142 (2006)> =2006ApJ...646..133M
ADC_Keywords: Clusters, galaxy ; Redshifts ; Photometry Keywords: galaxies: clusters: general - galaxies: elliptical and lenticular, cD - galaxies: evolution Abstract: We present spectroscopic confirmation of nine moderate-redshift galaxy groups and poor clusters selected from the ROSAT Deep Cluster Survey. The groups span the redshift range and have between 4 and 20 confirmed members. The velocity dispersions of these groups range from ∼125 to 650km/s. Similar to X-ray groups at low redshift, these systems contain a significant number of early-type galaxies. Therefore, the trend for X-ray-luminous groups to have high early-type fractions is already in place by at least z∼0.5. In four of the nine groups, the X-ray emission is clearly peaked on the most luminous early-type galaxy in the group. However, in several cases the central galaxy is composed of multiple luminous nuclei, suggesting that the brightest group galaxy may still be undergoing major mergers. In at least three (and possibly five) of the groups in our sample, a dominant early-type galaxy is not found at the center of the group potential. This suggests that many of our groups are not dynamically evolved despite their high X-ray luminosities. While similar systems have been identified at low redshift, the X-ray luminosities of the intermediate-redshift examples are 13 orders of magnitude higher than those of their low-redshift counterparts. We suggest that this may be evidence for group downsizing: while massive groups are still in the process of collapsing and virializing at intermediate redshifts, only low-mass groups are in the process of forming at the present day. Description: We select our intermediate-redshift group candidates from the ROSAT Deep Cluster Survey (RDCS; Rosati et al., 1998ApJ...492L..21R). All of the Palomar spectra were taken with the Carnegie Observatories Spectroscopic Multislit and Imaging Camera (COSMIC) spectrograph on the 5.1m Hale telescope between 1999 and 2001. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 51 169 *Photometric and spectroscopic results table2.dat 136 9 Group properties
Note on table1.dat: Galaxies identified as [MLF2006] JHHMMSS.ss+DDMMSS.s in Simbad.
See also: VII/84 : Groups of Galaxies. III. The CfA Survey (Geller+ 1983) VII/89 : Compact groups of compact galaxies (Shakhbazian+ 1973-1979) J/A+AS/100/47 : Lyon Groups of Galaxies (Garcia 1993) J/A+AS/117/39 : Hickson Compact Groups of Galaxies I. (Allam+, 1996) J/AJ/113/483 : Groups of Galaxies (Ramella+ 1997) J/A+AS/130/341 : Groups of Galaxies in PPS (Trasarti-Battistoni 1998) J/AJ/116/1573 : Redshift Survey Compact Groups (Barton+, 1998) J/A+A/342/1 : ESO Slice Project. VI. Groups of Galaxies. (Ramella+ 1999) J/AN/321/101 : Compact groups of galaxies in LCRS (Allam+, 2000) J/ApJ/534/114 : RASSCALS: X-ray and optical study (Mahdavi+, 2000) J/A+A/381/420 : Group of Galaxies in the SSRS2 catalog (Adami+, 2002) J/AJ/125/1660 : Distant compact groups from DPOSS (Iovino+, 2003) J/AJ/127/1811 : Catalog of SDSS compact groups of galaxies (Lee+, 2004) J/AJ/130/425 : Catalog of distant compact groups of galaxies (De Carvalho+, 2005) J/AN/327/365 : Clusters and groups of galaxies in 2dF (Tago+, 2006) J/A+A/479/927 : Group of galaxies in SDSS 5 (Tago+, 2008) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 2 I2 h RAh Hour of Right Ascension (J2000) 4- 5 I2 min RAm Minute of Right Ascension (J2000) 7- 11 F5.2 s RAs Second of Right Ascension (J2000) 13 A1 --- DE- Sign of the Declination (J2000) 14- 15 I2 deg DEd Degree of Declination (J2000) 17- 18 I2 arcmin DEm Arcminute of Declination (J2000) 20- 23 F4.1 arcsec DEs Arcsecond of Declination (J2000) 25- 28 F4.1 mag Rmag ? The R band magnitude 30 A1 --- f_Rmag  Composed Rmag (1) 32- 37 F6.4 --- z Spectroscopic redshift 39- 44 F6.4 --- e_z Error in z 46- 51 A6 --- ztype Redshift type (absorption and/or emission)
Note (1): '1' indicates that our ground-based data does not have high enough spatial resolution to separate out the three components, so the quoted magnitude is the total for all three components.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 15 A15 --- Group Group name (RX JHHMM.m+DDMM) 17- 18 I2 h RAh Right Ascension J2000 (hours) 20- 21 I2 min RAm Right Ascension J2000 (minutes) 23- 27 F5.2 s RAs Right Ascension J2000 (seconds) 29 A1 --- DE- Declination J2000 (sign) 30- 31 I2 deg DEd Declination J2000 (degrees) 33- 34 I2 arcmin DEm Declination J2000 (minutes) 36- 39 F4.1 arcsec DEs Declination J2000 (seconds) 42- 47 F6.4 --- z Group redshift 49- 50 I2 --- Nm Number of members in the group 53- 55 I3 km/s sig Velocity dispersion (Gaussian estimator) 57- 59 I3 km/s E_sig Error on sig (upper limit) 61- 63 I3 km/s e_sig Error on sig (lower limit) 65- 68 F4.2 --- ETf [0,1] Fraction of early-type galaxies 70-136 A67 --- Notes Remarks concerning the group (BGG = brightest group galaxy)
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Francois Ochsenbein [CDS] 02-May-2008
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