J/ApJ/805/160 Old star clusters in M101 from HST (Simanton+, 2015)
Two populations of old star clusters in the spiral galaxy M101 based on
HST/ACS observations.
Simanton L.A., Chandar R., Whitmore B.C.
<Astrophys. J., 805, 160 (2015)>
=2015ApJ...805..160S 2015ApJ...805..160S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Clusters, globular ; Photometry, HST
Keywords: galaxies: individual: M101;
galaxies: photometry; galaxies: star clusters: general
Abstract:
We present a new photometric catalog of 326 candidate globular
clusters (GCs) in the nearby spiral galaxy M101, selected from B, V,
and I Hubble Space Telescope Advanced Camera for Surveys images. The
luminosity function (LF) of these clusters has an unusually large
number of faint sources compared with GCLFs in many other spiral
galaxies. Accordingly, we separate and compare the properties of
"bright" (Mv←6.5) versus "faint" (Mv>-6.5; one magnitude fainter
than the expected GC peak) clusters within our sample. The LF of the
bright clusters is well fit by a peaked distribution similar to those
observed in the Milky Way (MW) and other galaxies. These bright
clusters also have similar size (reff) and spatial distributions as
MW GCs. The LF of the faint clusters, on the other hand, is well
described by a power law, dN(Lv)/dLv∝Lvα with
α=2.6±0.3, similar to those observed for young and
intermediate-age cluster systems in star forming galaxies. We find
that the faint clusters have larger typical reff than the bright
clusters, and have a flatter surface density profile, being more
evenly distributed, as we would expect for clusters associated with
the disk. We use the shape of the LF and predictions for mass-loss
driven by two-body relaxation to constrain the ages of the faint
clusters. Our results are consistent with two populations of old star
clusters in M101: a bright population of halo clusters and a fainter,
possibly younger, population of old disk clusters.
Description:
Ten pointings within M101 were taken with the HST/ACS Wide Field
Channel in 2002 November (Program ID: 9490, PI: K. Kuntz) using the
F435W (B), F555W (V), and F814W (I) filters. Each field covers
3.3'x3.4' (see Figure 1).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 58 326 M101 old star cluster catalog
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See also:
J/AJ/146/114 : Massive stars in M101. I. HST BVI photometry (Grammer+, 2013)
J/AJ/143/52 : Old star clusters in NGC 4449 from HST (Strader+, 2012)
J/ApJ/733/124 : Cepheids in M101 observed with HST (Shappee+, 2011)
J/MNRAS/403/429 : Candidate globular clusters in NGC 5170 (Forbes+, 2010)
J/A+A/507/1375 : HST/ACS VI data of M31 globular clusters (Perina+, 2009)
J/MNRAS/343/665 : VI photometry of globular cluster systems (Goudfrooij+, 2003)
J/A+AS/139/393 : Young Massive Star Clusters. II. (Larsen, 1999)
J/ApJS/122/431 : Star Clusters in M33 (Chandar+, 1999)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 I6 -- ID [945/271453] Identification Number
8- 9 I2 h RAh [14] Hour of Right Ascension (J2000)
11- 12 I2 min RAm [2/3] Minute of Right Ascension (J2000)
14- 18 F5.2 s RAs Second of Right Ascension (J2000)
20 A1 --- DE- [+] Sign of Declination (J2000)
21- 22 I2 deg DEd [54] Degree of Declination (J2000)
24- 25 I2 arcmin DEm [14/25] Arcminute of Declination (J2000)
27- 31 F5.2 arcsec DEs Arcsecond of Declination (J2000)
33- 37 F5.2 mag VMag [-9.5/-5.1] Absolute V band magnitude
39- 42 F4.2 mag B-V [0.5/1.5] The HST/ACS (B-V) color index
44- 47 F4.2 mag V-I [0.8/2.1] The HST/ACS (V-I) color index
49- 52 F4.2 mag B-I [1.3/3.4] The HST/ACS (B-I) color index
54- 58 F5.2 pc Rad [0.7/15.2]? Effective radius (1)
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Note (1): From the FWHM of each cluster, measured as described in the paper
and assuming a distance of 6.4Mpc to M101.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 17-Sep-2015