J/AJ/144/142 HST photometry of young stellar populations in M31 (Bianchi+, 2012)
A Hubble Space Telescope treasury study of star-forming regions in the Local
Group. II. Young stellar populations in M31.
Bianchi L., Efremova B., Hodge P., Kang Y.
<Astron. J., 144, 142 (2012)>
=2012AJ....144..142B 2012AJ....144..142B
ADC_Keywords: Galaxies, nearby ; Photometry, HST ; Stars, early-type
Keywords: dust, extinction - galaxies: individual: M31 - galaxies: structure -
galaxies: star clusters: general - galaxies: stellar content -
stars: early-type
Abstract:
We studied the young stellar populations of 22 star-forming regions in
the Andromeda galaxy (M31), with Hubble Space Telescope (HST)
multi-band imaging from far-UV to I. The regions were selected from
Galaxy Evolution Explorer (GALEX) wide-field far-UV imaging; they
sample different environments and galactocentric distances from 6 to
22kpc. They were imaged with 30 HST fields (360 distinct images, in
six bandpasses), with a pixel scale of 0.38pc projected on the sky, at
the distance of M31. This study is part of HST treasury survey program
HST-GO-11079, which includes star-forming regions in eight Local Group
galaxies. We provide a merged catalog of six-band stellar photometry
in the 30 M31 fields, containing 118036 sources brighter than V and
B∼23mag. Each HST field covers about 0.3kpc2 in M31, and contains up
to ∼7000 stars, of which the number varies by a factor of >7 among the
target regions; a large fraction of the sample are hot massive stars,
due to our choice of filters and exposures. We derived stellar
physical parameters and interstellar extinction for individual sources
by spectral energy distribution analysis with model-atmosphere colors,
and used the results to infer ages, massive stars content, and
extinction of the star-forming regions. Reddening is up to
E(B-V)≲0.6mag in some OB associations, and lowest in the outermost
regions (average of ≲0.12mag in OB184 at 21.9kpc). We examined the
spatial distribution (clustering) of the hot massive stars, and
defined OB associations on various spatial scales from compact to
wider, more spread out ones. A hierarchical structuring is observed,
with small compact groups arranged within large complexes. Their areas
vary from less than 10 to 105pc2, and masses are up to
~105M☉, in the scales sampled by our analysis. Their
cumulative mass distribution follows a power law, at least in part of
the sampled regime. Hot-star counts in the young regions compare very
well with integrated measurements of UV flux from GALEX.
Description:
The star-forming regions were chosen from the Galaxy Evolution
Explorer (GALEX) wide-field far-UV imaging.
Twenty-two star-forming regions in M31 were imaged with the WFPC2
camera on board the Hubble Space Telescope (HST) (30 distinct fields)
between 2007 July and 2008 June as part of treasury program HST-11079.
WFPC2 imaging in six broadband filters (F170W, F255W, F336W, F439W,
F555W, and F814W) was acquired at every pointing.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 123 30 HST observations
table2.dat 159 118036 HST photometry catalog
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
II/312 : GALEX-DR5 (GR5) sources from AIS and MIS (Bianchi+ 2011)
J/AJ/143/74 : HST photometry in 6 dwarf galaxies (Bianchi+, 2012)
J/ApJS/199/37 : GALEX catalog of star clusters in M31 (Kang+, 2012)
J/ApJ/730/88 : NGC 6822 star-forming regions from UV data (Efremova+, 2011)
J/ApJ/703/614 : UV star-forming regions in M31 (Kang+, 2009)
J/ApJS/173/185 : GALEX ultraviolet atlas of nearby galaxies (Gil de Paz+, 2007)
J/PASP/119/7 : HST WFPC2 star clusters in M31 (Krienke+, 2007)
J/AJ/133/2393 : UBVRI phot. in 7 Local Group dwarfs galaxies (Massey+, 2007)
J/AJ/131/2478 : M31 and M33 UBVRI photometry (Massey+, 2006)
J/ApJS/154/623 : M31 Long Period Variables : Photometry (Mould+, 2004)
J/AJ/122/2458 : M31 globular clusters from HST (Barmby+, 2001)
J/AJ/110/2715 : UBV photometry in NGC 6822, M31 and M33 (Massey+ 1995)
J/A+A/278/36 : M 31 new OB associations (Magnier+ 1993)
http://dolomiti.pha.jhu.edu/LocalGroup : Results from HST program 11079
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Fr Visit/field (1)
4- 26 A23 --- Field Field name
28- 37 F10.7 deg RAdeg Right Ascension in decimal degrees (J2000)
39- 47 F9.6 deg DEdeg Declination in decimal degrees (J2000)
49- 53 F5.2 kpc Dist Galactocentric distance
55- 61 A7 s T1 Exposure time in F170W
63- 73 A11 s T2 Exposure time in F255W
75- 81 A7 s T3 Exposure time in F336W
83- 89 A7 s T4 Exposure time in F439W
91- 95 A5 s T5 Exposure time in F555W
97-101 A5 s T6 Exposure time in F814W
103 I1 h RAh Hour of Right Ascension (J2000)
105-106 I2 min RAm Minute of Right Ascension (J2000)
108-111 F4.1 s RAs Second of Right Ascension (J2000)
113 A1 --- DE- Sign of the Declination
114-115 I2 deg DEd Degree of Declination (J2000)
117-118 I2 arcmin DEm Arcminute of Declination (J2000)
120-123 F4.1 arcsec DEs Arcsecond of Declination (J2000)
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Note (1): The archive data set names are "U9WQxxyyM" where "xx" is the
field/visit (e.g., 48, D8,...) and "yy" is the exposure in the
sequence of twelve exposures: yy = 01, 02, 03, 04, 05, 06, 07, 08, 09,
0A, 0B, 0C); for example: U9WQ4901M, U9WQ4902M,... U9WQ490CM. Data can
be downloaded from the MAST archive
(http://archive.stsci.edu/hst/search.php). Catalogs and combined
images can also be obtained from the author's Web site (
http://dolomiti.pha.jhu.edu/LocalGroup).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- Seq [0/118035] Running sequence number
<[BEH2012] M31 NNNNNN> in Simbad
8- 10 A3 --- Gal [M31] Parent galaxy name (M31)
12- 27 A16 --- IAU Source IAU identifier (JHHMMSS.s+DDMMSS)
29- 38 F10.7 deg RAdeg Right Ascension in decimal degrees (J2000) (1)
40- 49 F10.7 deg DEdeg Declination in decimal degrees (J2000) (1)
51- 55 F5.2 mag F170W ?=99 HST/WFPC2 F170W band Vega magnitude (2)
57- 61 F5.2 mag e_F170W ?=99 Error in F170Wmag
63- 67 F5.2 mag F225W ?=99 HST/WFPC2 F225W band Vega magnitude (2)
69- 73 F5.2 mag e_F225W ?=99 Error in F225Wmag
75- 79 F5.2 mag F336W ?=99 HST/WFPC2 F336W band Vega magnitude (2)
81- 85 F5.2 mag e_F336W ?=99 Error in F336Wmag
87- 91 F5.2 mag F439W ?=99 HST/WFPC2 F439W band Vega magnitude (2)
93- 97 F5.2 mag e_F439W ?=99 Error in F439Wmag
99-103 F5.2 mag F555W ?=99 HST/WFPC2 F555W band Vega magnitude (2)
105-109 F5.2 mag e_F555W ?=99 Error in F555Wmag
111-115 F5.2 mag F814W ?=99 HST/WFPC2 F814W band Vega magnitude (2)
117-121 F5.2 mag e_F814W ?=99 Error in F814Wmag
123-127 F5.2 mag Umag ?=99 The U band Vega magnitude (2)
129-133 F5.2 mag Bmag ?=99 The B band Vega magnitude (2)
135-139 F5.2 mag Vmag ?=99 The V band Vega magnitude (2)
141-145 F5.2 mag Imag ?=99 The I band Vega magnitude (2)
147-152 F6.3 --- Sharp Sharpness parameter of HSTphot
154 I1 --- Tp [1/5] HSTphot type of the source
(1=good star, 2, 4 or 5) (3)
156-157 A2 --- Fr The visit/field from Table 1
159 I1 --- Ch [0/3] WFPC2 detector (0=PC, 1=WF2, 2=WP3, 3=WF4)
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Note (1): Coordinate shifts have been added to fields as below:
D8: δRAdeg=-0.00013°, δDEdeg=-0.00018°;
E1: {delat}RAdeg=0.0001°, δDEdeg=-0.00003°;
E8: δRAdeg=-0.0001°, δDEdeg=0.0002°;
F0: δRAdeg=0.00016°, δDEdeg=-0.00017°.
Note (2): The UBVI magnitudes were transformed from the F336W, F439W,
F555W, and F814Wmagnitudes to the Johnson UBVI with HSTphot
(photometry package by Dolphin, 2000PASP..112.1383D 2000PASP..112.1383D). Sources detected
in either F439W or F555W and at least another band are included;
however sources not detected in F555W should be discarded (mostly
artifacts) as explained in section 3.2; only sources with Tp=1 and
Sharp in range [-0.3/+0.3] should be used for analysis; sources with
any HSTphot Type and Sharp are included for completeness.
Note (3): HSTphot types are:
1 = good star;
2 = unresolved binary;
5 = extended objects.
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History:
From electronic version of the journal
References:
Bianchi et al, Paper I, 2012AJ....143...74B 2012AJ....143...74B, Cat. J/AJ/143/74
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 11-Dec-2013