J/ApJ/582/668 Colours and Hα in galaxy pairs (Barton Gillespie+, 2003)
Tidally triggered star formation in close pairs of galaxies.
II. Constraints on burst strengths and ages.
Barton Gillespie E., Geller M.J., Kenyon S.J.
<Astrophys. J. 582, 668 (2003)>
=2003ApJ...582..668B 2003ApJ...582..668B
ADC_Keywords: Galaxy catalogs ; Redshifts ; Galaxies, photometry ;
Equivalent widths
Keywords: galaxies: evolution - galaxies: fundamental parameters -
galaxies: interactions - galaxies: kinematics and dynamics -
galaxies: structure
Abstract:
Galaxy-galaxy interactions rearrange the baryons in galaxies and
trigger substantial star formation; the aggregate effects of these
interactions on the evolutionary histories of galaxies in the universe
are poorly understood. We combine B- and R-band photometry and optical
spectroscopy to estimate the strengths and timescales of bursts of
triggered star formation in the centers of 190 galaxies in pairs and
compact groups. Based on an analysis of the measured colors and
EW(Hα), we characterize the preexisting and triggered
populations separately. The best-fitting burst scenarios assume
stronger reddening corrections for line emission than for the
continuum and continuous star formation lasting for ≳100Myr. The most
realistic scenarios require an initial mass function that is deficient
in the highest mass stars. The color of the preexisting stellar
population is the most significant source of uncertainty. Triggered
star formation contributes substantially (probably ≳50%) to the
R-band flux in the central regions of several galaxies; tidal tails do
not necessarily accompany this star formation. Many of the galaxies in
our sample have bluer centers than outskirts, suggesting that pre- or
nonmerger interactions may lead to evolution along the Hubble
sequence. These objects would appear blue and compact at higher
redshifts; the older, redder outskirts of the disks would be difficult
to detect. Our data indicate that galaxies with larger separations on
the sky contain weaker, and probably older, bursts of star formation
on average. However, confirmation of these trends requires further
constraints on the colors of the older stellar populations and on the
reddening for individual galaxies.
Description:
In this paper, we concentrate on the photometric properties of the
galaxies in the overlap of the spectroscopic and photometric samples
(190 galaxies comprising all or part of 78 pairs and 13 compact
groups; hereafter the SP sample). We have Hα rotation curves
for 103 of these galaxies; 89 provide useful measurements of Vc, the
velocity width.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 80 190 *The SP Sample
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Note on table1.dat: Galaxies identified as [BGK2003] HHMMSS.s+DDMMSS in Simbad.
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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 Hour of Right Ascension (B1950)
4- 5 I2 min RAm Minute of Right Ascension (B1950)
7- 10 F4.1 s RAs Second of Right Ascension (B1950)
12 A1 --- DE- Sign of the Declination (B1950)
13- 14 I2 deg DEd Degree of Declination (B1950)
16- 17 I2 arcmin DEm Arcminute of Declination (B1950)
19- 20 I2 arcsec DEs Arcsecond of Declination (B1950)
22 I1 --- NGal Number of galaxies in system
24- 28 I5 km/s cz Redshift
30- 33 F4.1 kpc DSep Pair separation on the sky in units of kpc/h (1)
35- 37 I3 km/s VSep Velocity separation of pair (2)
39- 44 F6.2 mag RMAG Absolute R band magnitude (3)
46- 48 A3 --- f_RMAG Flag on RMAG (4)
50- 53 F4.2 mag B-R The (B-R) color of the galaxy portion on the
slit during the spectroscopic observation (5)
55- 59 F5.1 0.1nm EWHA The Hα equivalent width
61- 64 F4.2 --- Balmer ? Balmer decrement corrected for Balmer
absorption, Hα/Hβ (6)
66- 70 F5.1 km/s VWid ? Corrected velocity width
72- 75 A4 --- RotDes A rotation curve description (7)
77- 80 A4 --- Fig Label for Figures 23 and 24
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Note (1): Or distance to closest galaxy in n-tuple.
Note (2): Or velocity difference to closest galaxy in velocity within
the n-tuple.
Note (3): Extrapolated to the total magnitude and measured assuming
Note (4): Flag for R absolute magnitude:
a = Image was calibrated from a shorter exposure;
b = Galaxies overlapped;
c = Bright star in background, or smaller but significant star(s)
on galaxy.
Note (5): Corrected for Galactic extinction and nebular lines.
Note (6): Corrected for Balmer absorption
Note (7): Rotation curve descriptions:
norm = normal
marg = marginal (intermediate between normal and distorted)
dist = distorted (see text of Barton et al., 2001ApJ...550L..35B 2001ApJ...550L..35B)
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History:
From electronic version of the journal
References:
Barton et al., Paper I 2000ApJ...530..660B 2000ApJ...530..660B
(End) Greg Schwarz [AAS], Patricia Bauer [CDS] 26-Mar-2003