J/AJ/143/52 Old star clusters in NGC 4449 from HST imaging (Strader+, 2012)
Old massive globular clusters and the stellar halo of the dwarf starburst
galaxy NGC 4449.
Strader J., Seth A.C., Caldwell N.
<Astron. J., 143, 52 (2012)>
=2012AJ....143...52S 2012AJ....143...52S
ADC_Keywords: Galaxies, nearby ; Clusters, globular ; Photometry, HST ;
Radial velocities ; Cross identifications
Keywords: galaxies: individual (NGC 4449) - galaxies: star clusters: general -
globular clusters: general - galaxies: formation - galaxies: evolution
Abstract:
We use Hubble Space Telescope imaging to show that the nearby dwarf
starburst galaxy NGC 4449 (=UGC 7592) has an unusual abundance of
luminous red star clusters. Joint constraints from integrated
photometry, low-resolution spectroscopy, dynamical mass-to-light
ratios, and resolved color-magnitude diagrams provide evidence that
some of these clusters are old globular clusters (GCs). Spectroscopic
data for two massive clusters suggest intermediate metallicities
([Fe/H]~-1) and subsolar Mg enhancement ([Mg/Fe]~-0.1 to -0.2). One of
these clusters may be the nucleus of a tidally disrupting dwarf
galaxy; the other is very massive (∼3*106M☉). We have also
identified a population of remote halo GCs. NGC 4449 is consistent
with an emerging picture of the ubiquity of stellar halos among dwarf
galaxies, and study of its GCs may help distinguish between accretion
and in situ scenarios for such halos.
Description:
Annibali et al. (2008AJ....135.1900A 2008AJ....135.1900A) imaged NGC 4449 in 2005 November
with the Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS)
in the F435W, F555W, and F814W broadband filters. Table 1 lists our
catalog of 106 clusters, including 88 candidates of good quality and
18 less convincing "possible" clusters.
We targeted clusters for follow-up MMT/Hectospec spectroscopy from the
HST/ACS catalog (Annibali et al. 2008AJ....135.1900A 2008AJ....135.1900A) and from the
SDSS-DR6 (Cat. II/282). For the Hectospec observations, we used the
270l/mm grating, which gave spectral coverage from 3650 to 9200Å
and a resolution of ∼6Å. The same configuration was observed on two
different nights in 2009 May. For a very similar target catalog,
MMT/Hectochelle high-resolution spectra were also taken with a
resolution R∼34000.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 76 106 HST/ACS star cluster photometry
table3.dat 38 31 Heliocentric radial velocities
table4.dat 82 13 SDSS candidate globular clusters with spectroscopy
table5.dat 82 7 Additional SDSS photometric globular cluster
candidates
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
J/AJ/141/61 : Star clusters in M31. II. (Caldwell+, 2011)
J/AJ/142/129 : HST photometry of NGC 4449 clusters (Annibali+, 2011)
J/ApJ/741/86 : XRBs and star clusters in NGC 4449 (Rangelov+, 2011)
J/MNRAS/392/879 : Globular clusters in nearby dwarf galaxies (Georgiev+, 2009)
J/AZh/85/794 : UBVRHα photometry on 5 galaxies (Gusev+, 2008)
J/AJ/124/3157 : Velocities in NGC 4449 (Valdez-Gutierrez+, 2002)
J/A+AS/139/491 : BVI photometry of nearby galaxies (Makarova+, 1999)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1 A1 --- C [CP] Confirmed or Possible cluster (C or P)
3- 5 A3 --- ID Cluster identification (A = East HST/ACS
pointing; B = West HST/ACS pointing)
<[SSC2012] ANN> in Simbad (1)
7- 16 F10.6 deg RAdeg [186.97/187.113] Right Ascension (J2000)
18- 26 F9.6 deg DEdeg [44.0529/44.1440] Declination (J2000)
28- 31 F4.2 arcsec Aper [0.39/2.8] Aperture radius for photometry
33- 36 F4.2 arcsec Rh [0.1/0.9] Half-light radius direct estimate
38- 42 F5.2 mag Vmag [15.46/22.9] HST/ACS F555W band magnitude (2)
44- 47 F4.2 mag e_Vmag Uncertainty in F555W (2)
49- 52 F4.2 mag B-V (F435W-F555W) color index (2)
54- 57 F4.2 mag V-I (F555W-F814W) color index (2)
59- 63 A5 --- Age Photometric cluster age: "Young" (≲1Gyr) or "Old"
65- 66 I2 --- G01 ? Gelatt et al. (2001PASP..113..142G 2001PASP..113..142G) identifier
(<[GHG2001] NN> in Simbad) (4)
68- 69 I2 --- A11 ? Annibali et al. (Cat. J/AJ/142/129) identifier
(<[ATA2011] NN> in Simbad) (4)
70- 72 A3 --- f_A11 [SSC] SSC: central super star cluster
74- 76 I3 --- R11 ? Rangelov et al. (Cat. J/ApJ/741/86) identifier
(<[RPC2011] NNN> in Simbad) (4)
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Note (1): B13 and B15 are too close to the center of the galaxy for proper
photometry in the SDSS-DR6 photometric catalog (Cat. II/282). See
integrated photometry from SDSS images and Spitzer/IRAC in table 7
(section 5.2).
Note (2): Magnitudes are given on the Vega system with the appropriate zero
points taken from the ACS Web site (F435W=25.793, F555W=25.744,
F814W=25.536).
F555W magnitudes are very close to the standard V band and we use the
two interchangeably.
Note (4): Gelatt et al.(2001PASP..113..142G 2001PASP..113..142G) previously identified candidate
clusters within a smaller HST/Wide Field Planetary Camera 2 (WFPC2)
pointing; these IDs are cross-referenced along with those of
Annibali et al. (Cat. J/AJ/142/129) and Rangelov et al. 2011
(Cat. J/ApJ/741/86).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- ID Cluster identification (1)
6- 15 F10.6 deg RAdeg [186.946/187.207] Right Ascension (J2000)
17- 25 F9.6 deg DEdeg [43.9875/44.2173] Declination (J2000)
27- 31 F5.1 km/s HRV [103.5/299.4] Heliocentric radial velocities
33- 36 F4.1 km/s e_HRV Uncertainty on HRV
38 A1 --- f_HRV [SC] Source (S or C) (2)
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Note (1): Identification as:
A = East HST/ACS pointing <[SSC2012] ANN> in Simbad
B = West HST/ACS pointing <[SSC2012] BNN> in Simbad
S = From SDSS-DR6 imaging data (Cat. II/282) <[SSC2012] SNNN> in Simbad
Note (2): Source as follows:
C = "Chelle" (radial velocity from MMT/Hectochelle)
S = "Spec" (radial velocity from MMT/Hectospec)
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Byte-by-byte Description of file: table[45].dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- ID Cluster candidate identification (1)
6- 15 F10.6 deg RAdeg [186.8947/187.2062] Right Ascension (J2000)
17- 25 F9.6 deg DEdeg [43.9875/44.2173] Declination (J2000)
27- 31 F5.2 mag umag [19.97/22.62] SDSS u magnitude
33- 36 F4.2 mag e_umag Uncertainty on u magnitude
38- 42 F5.2 mag gmag [18.84/20.82] SDSS g magnitude
44- 47 F4.2 mag e_gmag Uncertainty on g magnitude
49- 53 F5.2 mag rmag [18.31/20.3] SDSS r magnitude
55- 58 F4.2 mag e_rmag Uncertainty on r magnitude
60- 64 F5.2 mag imag [18.14/20.68] SDSS i magnitude
66- 69 F4.2 mag e_imag Uncertainty on i magnitude
71- 75 F5.2 mag zmag [18.11/21.02] SDSS z magnitude
77- 80 F4.2 mag e_zmag Uncertainty on z magnitude
82 I1 --- C [1/5]? cluster classification (2)
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Note (1): Designation of the clusters:
* <[SSC2012] SNNN> in Simbad for spectroscopic candidates (table 4)
* <[SSC2012] SCN> in Simbad for photometric additional candidates (table 5);
SC1 is confirmed from HST data.
Note (2): Classification of cluster as follows:
1 = confirmed globular cluster;
2 = probable globular cluster;
3 = possible globular cluster;
4 = foreground star or young cluster;
5 = young cluster.
blank = photometric globular cluster candidate
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 23-Apr-2013