J/ApJ/770/137 UV star clusters in 4 elliptical galaxies (Ford+, 2013)
Direct detections of young stars in nearby elliptical galaxies.
Ford H.A., Bregman J.N.
<Astrophys. J., 770, 137 (2013)>
=2013ApJ...770..137F 2013ApJ...770..137F
ADC_Keywords: Galaxies, nearby ; Photometry, ultraviolet
Keywords: galaxies: elliptical and lenticular, cD;
galaxies: star clusters: general; galaxies: star formation;
ultraviolet: galaxies; ultraviolet: stars
Abstract:
Small amounts of star formation in elliptical galaxies are suggested
by several results: surprisingly young ages from optical line indices,
cooling X-ray gas, and mid-infrared dust emission. Such star formation
has previously been difficult to directly detect, but using
ultraviolet Hubble Space Telescope Wide Field Camera 3 imaging, we
have identified individual young stars and star clusters in four
nearby ellipticals. Ongoing star formation is detected in all
galaxies, including three ellipticals that have previously exhibited
potential signposts of star-forming conditions (NGC 4636, NGC 4697,
and NGC 4374), as well as the typical "red and dead" NGC 3379. The
current star formation in our closest targets, where we are most
complete, is between 2.0 and 9.8x10-5M☉/yr. The star formation
history was roughly constant from 0.5 to 1.5 Gyr (at
(3-5)x10-4M☉/yr), but decreased by a factor of several in the
past 0.3Gyr. Most star clusters have a mass between 102 and
104M☉. The specific star formation rates of ∼10-16/yr (at
the present day) or ∼10-14/yr (when averaging over the past Gyr)
imply that a fraction 10-8 of the stellar mass is younger than
100Myr and 10-5 is younger than 1Gyr, quantifying the level of
frosting of recent star formation over the otherwise passive stellar
population. There is no obvious correlation between either the
presence or spatial distribution of postulated star formation
indicators and the star formation we detect.
Description:
Observations were conducted using HST's WFC3 between 2009 November 23
and 2010 March 29 (Cycle 17, PID 11583). These observations were made
using UVIS through two filters, F225W and F336W.
The detected sources are best explained as being individual star
clusters with masses between 102 and 104M☉ and ages less
than 1Gyr: they are radially concentrated about the center of each
galaxy, ruling out background contamination; they are too bright to be
p-AGB stars from the dominant old population and too red as a
population to be p-AGB stars from an intermediate-age population; and
the absence of a large number of bright main sequence turnoff stars
precludes a large enough population of blue loop stars to account for
any but a tiny fraction of the observed sources.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 115 271 Properties of UV-bright clusters
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/ApJ/768/137 : Color-metallicity relations. IV. M84 GCs (Yoon+, 2013)
J/ApJ/759/116 : Chemical analysis of NGC 4636 globular clusters (Park+, 2012)
J/A+A/544/A115 : Velocities of NGC 4636 globular clusters (Schuberth+, 2012)
J/A+A/438/1163 : Catalogue of Open Cluster Data (COCD) (Kharchenko+, 2005)
J/A+A/433/43 : C-T1 phot. of NGC 4636 GC system (Dirsch+, 2005)
J/AJ/129/2138 : Centers of early-type galaxies with HST (Lauer+, 2005)
J/MNRAS/363/769 : Dynamical modelling of 4 early-type gal. (Samurovic+, 2005)
J/MNRAS/345/949 : UBRI photometry of NGC 3379 GCs (Whitlock+, 2003)
J/ApJS/127/39 : Stellar & gas kinematics in early-type galaxies (Caon+ 2000)
J/A+AS/96/269 : Stellar Models from 0.8 to 120 Msolar (Schaller+, 1992)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/271] Cluster ID number
5- 7 A3 --- --- [NGC]
9- 12 I4 --- Name Host galaxy NCG name (3379, 4697, 4636 or 4374)
14- 15 I2 h RAh Hour of Right Ascension (J2000)
17- 18 I2 min RAm Minute of Right Ascension (J2000)
20- 25 F6.3 s RAs Second of Right Ascension (J2000)
27 A1 --- DE- Sign of the Declination (J2000)
28- 29 I2 deg DEd Degree of Declination (J2000)
31- 32 I2 arcmin DEm Arcminute of Declination (J2000)
34- 38 F5.2 arcsec DEs Arcsecond of Declination (J2000)
40- 44 F5.2 mag F225W [21.9/25.6] HST/WFC3 F225W band magnitude
46- 49 F4.2 mag e_F225W [0.02/0.4] Uncertainty in F225Wmag
51- 55 F5.2 mag F336W [21/26.2] HST/WFC3 F336W band magnitude
57- 60 F4.2 mag e_F336W Uncertainty in F336Wmag
62- 66 F5.2 mag col [-2.3/1] The (F225W-F336W) color index
68- 71 F4.2 mag e_col Uncertainty in color
73- 78 E6.3 Msun Mass [100/30000]? Cluster mass
80- 86 E7.3 Msun E_Mass [0/15900]? Upper uncertainty in Mass
88- 93 E6.3 Msun e_Mass [0/19200]? Lower uncertainty in Mass
95-100 E6.3 yr Age ? Cluster age
102-108 E7.3 yr E_Age ? Upper uncertainty in Age
110-115 E6.3 yr e_Age ? Lower uncertainty in Age
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 13-Jan-2015