J/AJ/125/2427 1.4GHz flux densities of Abell 2255 galaxies (Miller+, 2003)
Abell 2255: increased star formation and AGN activity in a
cluster-cluster merger.
Miller N.A., Owen F.N.
<Astron. J., 125, 2427-2446 (2003)>
=2003AJ....125.2427M 2003AJ....125.2427M
ADC_Keywords: Clusters, galaxy ; Galaxies, radio ; Radial velocities
Keywords: galaxies: clusters: general - galaxies: evolution - radio continuum -
galaxies: clusters: individual (Abell 2255)
Abstract:
Deep VLA 1.4GHz radio continuum imaging of Abell 2255 is presented.
This cluster is among the better nearby candidates for rich
cluster-cluster merger systems, with evidence including an elongated
X-ray morphology, the presence of a radio halo, and substructure
present in its galaxy distribution. Our radio observations reach an
rms sensitivity of ∼40µJy/beam, enabling us to detect (at 5σ)
star formation rates as low as 1.4M☉/yr from the center of the
cluster out to a radial distance of 3h-175Mpc. The radio data are
complemented by optical imaging and a large spectroscopic database,
allowing us to separate all galaxies with MRc≤-20 0 into cluster
members and foreground/background galaxies. The spectra are also used
to associate the galaxies' radio emission with either star formation
or active galactic nuclei (AGNs). We compare the resulting cluster
radio galaxy population with those of 19 other nearby Abell clusters
and find strong evidence for an increase in the frequency of radio
galaxies in Abell 2255. This increase is seen in two separate types of
galaxies: powerful radio AGNs and optically faint star-forming
galaxies. The optical spectra of the latter often indicate current or
recent starbursts, and these galaxies appear to be distributed along
an axis perpendicular to the probable merger axis. We assess these
factors in light of models of galaxy evolution and suggest that the
cluster-cluster merger is responsible for triggering galaxy activity
in Abell 2255.
Description:
Radio observations at 1.4GHz were made with the VLA in two
configurations. The higher resolution observations were performed
during 1998 July while the VLA was in its B configuration, and lower
resolution observations were performed during 1999 May in the D
configuration.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 73 46 Cluster radio galaxies
table2.dat 68 36 Additional radio galaxies
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See also:
J/AJ/123/567 : SDSS quasar catalog, I: Early Data Release (Schneider+, 2002)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (J2000.0) (G1)
4- 5 I2 min RAm Right ascension (J2000.0) (G1)
7- 10 F4.1 s RAs Right ascension (J2000.0) (G1)
12 A1 --- DE- Declination sign (J2000.0) (G1)
13- 14 I2 deg DEd Declination (J2000.0) (G1)
16- 17 I2 arcmin DEm Declination (J2000.0) (G1)
19- 20 I2 arcsec DEs Declination (J2000.0) (G1)
22- 26 I5 km/s cz Heliocentric radial velocity (1)
28- 29 I2 km/s e_cz rms uncertainty on cz
31- 35 F5.2 mag Rcmag Cousins R magnitude, calculated for the
Gunn-Oke aperture, with an error of ≲0.05mag
37- 40 F4.2 Mpc Dist Radial distance (2)
42- 48 F7.3 mJy S1.4GHz Flux density at 1.4GHz
50- 54 F5.3 mJy e_S1.4GHz rms uncertainty on S1.4GHz
56- 58 F3.1 arcsec Sep ? Separation betwen optical and radio emission
59 A1 --- n_Sep [c] Note on Sep (3)
61- 64 A4 --- Class Classification (4)
66 A1 --- n_Class [b] Note on Class (5)
68- 71 A4 --- Morph Morphology
73 A1 --- n_Morph Note on Morph (6)
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Note (1): All velocities and associated errors have been taken from
Paper I (Hill et al., 2003, in prep.), which includes SDSS EDR
(Schneider et al., 2002, Cat. J/AJ/123/567) data.
Note (2): Radial distances are calculated based on a central position
of RA = 17 12 45 (J2000.0) DE = +64 03 54.
Note (3): Note on Sep:
c: See Figs. 2-6 of the paper.
Note (4): The classes are determined from the galaxy spectra and
are defined as follows:
SF: star-forming galaxy
AGNl: AGNs with optical spectrum dominated by an old stellar
population but with weak emission of [N II] and
sometimes [S II]
AGNo: AGNs with pure absorption-line spectrum representative of old
stellar population stars
AGNs: AGNs with emission-line spectrum (Seyfert)
Note (5): Note on Class:
b: The lack of optical emission lines formally places this galaxy in
the AGN category. However, there is evidence that these galaxies
are heavily dust-obscured star-forming galaxies (see text).
Note (6): Note on Morph:
a: Hδ absorption is sufficient for classification as an e(a)
galaxy, but measurement is noisy and we tentatively classify the
galaxy as e(c).
d: Wavelength coverage of spectrum misses [O II]; strong emission
lines suggest this is a potential e(b) galaxy.
e: Potential k + a galaxy, although spectrum is relatively noisy
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (J2000.0) (G1)
4- 5 I2 min RAm Right ascension (J2000.0) (G1)
7- 10 F4.1 s RAs Right ascension (J2000.0) (G1)
12 A1 --- DE- Declination sign (J2000.0) (G1)
13- 14 I2 deg DEd Declination (J2000.0) (G1)
16- 17 I2 arcmin DEm Declination (J2000.0) (G1)
19- 20 I2 arcsec DEs Declination (J2000.0) (G1)
22- 27 I6 km/s cz Heliocentric radial velocity (1)
28- 29 A2 --- n_cz Reference and notes for cz (2)
31- 33 I3 km/s e_cz rms uncertainty on cz
35- 39 F5.2 mag Rcmag ? Cousins R magnitude, calculated for the
Gunn-Oke aperture, with an error of ≲0.05mag
41- 47 F7.3 mJy S1.4GHz Flux density at 1.4GHz
49- 53 F5.3 mJy e_S1.4GHz rms uncertainty on S1.4GHz
55- 57 F3.1 arcsec Sep ? Separation
59- 62 A4 --- Class Classification (3)
64- 68 A5 --- Notes Notes (4)
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Note (1): All velocities and associated errors have been taken from
Paper I (Hill et al., 2003, in prep.), unless otherwise noted.
Note (2): References for cz, if not Paper I:
b: velocity and error from Strauss et al. (1992, Cat. II/174).
Galaxy pair (UGC 10731 or VV726), where each galaxy is a radio
source but the flux measurement and velocity correspond to the
system.
e: velocity and error taken from the SDSS EDR (Cat. J/AJ/123/567).
j: See Fig. 7 of the paper
Note (3): The classes are determined from the galaxy spectra and are defined as
follows:
SF: star-forming galaxy
AGNl: AGNs with optical spectrum dominated by an old stellar
population but with weak emission of [N II] and
sometimes [S II]
AGNo: AGNs with pure absorption-line spectrum representative of old
stellar population stars
AGNs: AGNs with emission-line spectrum (Seyfert)
QSO: quasar designation from SDSS EDR.
Note that J170902+641728, J170911+632940, J171010+642257,
J171118+643902, and J171346+641447 are compact starbursts
misidentified as QSOs by the automated routines of the SDSS EDR. False
identifications of this type are among the principal contaminants of
the SDSS QSO sample (Richards et al., 2002AJ....123.2945R 2002AJ....123.2945R).
Note (4): Notes:
a: Background galaxy.
c: Foreground galaxy.
d: Outside the 3 Mpc radial limit of the study.
f: Cluster member.
g: Optical magnitude too faint to be formally included in the
radio galaxy study.
h: See Fig. 8 of the paper.
i: The SDSS velocity for this galaxy was flagged because of
inconsistent measurements by their automated routines. Inspection
of the spectrum and a prior velocity measurement from NED clearly
indicate it is consistent with cluster membership.
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Global notes:
Note (G1):
Galaxies are identified as [MO2003] JHHMMSS.s+DDMMSS in Simbad
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History:
From electronic version of the journal
(End) James Marcout, Patricia Bauer [CDS] 09-Feb-2004