J/ApJ/768/137 HST photometry of M84 globular clusters (Yoon+, 2013)
Nonlinear color-metallicity relations of globular clusters.
IV. Testing the nonlinearity scenario for color bimodality via HST/WFC3 u-band
photometry of M84 (NGC 4374).
Yoon S.-J., Sohn S.T., Kim H.-S., Chung C., Cho J., Lee S.-Y.,
Blakeslee J.P.
<Astrophys. J., 768, 137 (2013)>
=2013ApJ...768..137Y 2013ApJ...768..137Y
ADC_Keywords: Clusters, globular ; Photometry, HST
Keywords: galaxies: clusters: general; galaxies: formation;
galaxies: individual (M84, M87); stars: horizontal-branch
Abstract:
Color distributions of globular clusters (GCs) in most massive
galaxies are bimodal. Assuming linear color-to-metallicity
conversions, bimodality is viewed as the presence of merely two GC
subsystems with distinct metallicities, which serves as a critical
backbone of various galaxy formation theories. Recent studies,
however, revealed that the color-metallicity relations (CMRs) often
used to derive GC metallicities (e.g., CMRs of g-z, V-I, and C-T1)
are in fact inflected. Such inflection can create bimodal color
distributions if the underlying GC metallicity spread is simply broad
as expected from the hierarchical merging paradigm of galaxy
formation. In order to test the nonlinear-CMR scenario for GC color
bimodality, the u-band photometry is proposed because the u-related
CMRs (e.g., CMRs of u-g and u-z) are theoretically predicted to be
least inflected and most distinctive among commonly used optical CMRs.
Here, we present Hubble Space Telescope (HST)/WFC3 F336W (u-band)
photometry of the GC system in M84, a giant elliptical in the Virgo
galaxy cluster. Combining the u data with the existing HST ACS/WFC g
and z data, we find that the u-z and u-g color distributions are
different from the g-z distribution in a very systematic manner and
remarkably consistent with our model predictions based on the
nonlinear-CMR hypothesis. The results lend further confidence to the
validity of the nonlinear-CMR scenario as an explanation for GC color
bimodality. There are some GC systems showing bimodal spectroscopic
metallicity, and in such systems the inflected CMRs often create
stronger bimodality in the color domain.
Description:
In this paper, we perform the Hubble Space Telescope (HST)/WFC3
archival F336W (u-band) photometry for the M84 (NGC 4374) GC system.
The M84 images were observed as part of the science program GO-11583
(PI: J. Bregman).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 65 390 The u-, g-, and z-band mags and their observational
errors for the M84 globular cluster candidates
--------------------------------------------------------------------------------
See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/ApJ/763/40 : UBVI phot. of GCs in the Fornax galaxy cluster (Kim+, 2013)
J/MNRAS/426/1475 : CaT in 903 globular clusters (Usher+, 2012)
J/MNRAS/416/155 : Globular clusters in 5 early-type galaxies (Faifer+, 2011)
J/A+A/525/A19 : Phot. of globulars in early galaxies (Chies-Santos+, 2011)
J/ApJ/743/149 : Color-metallicity relations. Paper II: M87 GCs (Yoon+, 2011)
J/ApJS/180/54 : GC candidates in ACS Virgo survey. (Jordan+, 2009)
J/MNRAS/389/1150 : Spitzer phot. of globulars in 2 galaxies (Spitler+, 2008)
J/ApJS/171/101 : GCs in the ACS Virgo cluster survey (Jordan+, 2007)
J/ApJS/154/509 : ACS Virgo Cluster Survey. II. (Jordan+, 2004)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/390] Globular cluster index number
5- 15 F11.7 deg RAdeg Right Ascension in decimal degrees (J2000)
17- 26 F10.7 deg DEdeg Declination in decimal degrees (J2000)
28- 33 F6.3 mag umag [22.5/27.9] HST/WFC3 F336W band extinction
corrected AB magnitude
35- 39 F5.3 mag e_umag [0.008/0.5] Error in umag
41- 46 F6.3 mag gmag HST/ACS F475W band extinction corrected
AB magnitude from Jordan et al. 2009
(J/ApJS/180/54)
48- 52 F5.3 mag e_gmag Error in gmag
54- 59 F6.3 mag zmag [19.5/25.2] HST/ACS F850LP band extinction
corrected AB magnitude from Jordan et al. 2009
(J/ApJS/180/54)
61- 65 F5.3 mag e_zmag [0.005/0.2] Error in zmag
--------------------------------------------------------------------------------
Nomenclature note:
The globular clusters are <[JPB2009] DDD.ddddddd+DD.ddddddd> in Simbad.
History:
From electronic version of the journal
References:
Yoon et al. Paper I. 2006Sci...311.1129Y 2006Sci...311.1129Y
Yoon et al. Paper II. 2011ApJ...743..149Y 2011ApJ...743..149Y Cat. J/ApJ/743/149
Yoon et al. Paper III. 2011ApJ...743..150Y 2011ApJ...743..150Y
Kim et al. Paper V. 2013ApJ...768..138K 2013ApJ...768..138K
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 28-Nov-2014