J/AJ/143/74 HST photometry in 6 dwarf galaxies (Bianchi+, 2012)
A treasury study of star-forming regions in the Local Group.
I. HST photometry of young populations in six dwarf galaxies.
Bianchi L., Efremova B., Hodge P., Massey P., Olsen K.A.G.
<Astron. J., 143, 74 (2012)>
=2012AJ....143...74B 2012AJ....143...74B
ADC_Keywords: Galaxies, nearby ; Photometry, HST ; Ultraviolet ;
Stars, early-type
Keywords: dust, extinction - galaxies: individual (NGC 6822, WLM, Pegasus,
Phoenix, Sextans A, Sextans B) - galaxies: star clusters: general -
galaxies: stellar content - stars: early-type - ultraviolet: galaxies
Abstract:
We present a comprehensive study of young stellar populations in six
dwarf galaxies in or near the Local Group: Phoenix, Pegasus,
Sextans A, Sextans B, WLM, and NGC 6822. Their star-forming regions,
selected from GALEX wide-field far-UV imaging, were imaged (at sub-pc
resolution) with the WFPC2 camera on board the Hubble Space Telescope
(HST) in six bandpasses from far-UV to IR to detect and characterize
their hot massive star content. This study is part of HST treasury
survey program HST-GO-11079; the general data characteristics and
reduction procedures are detailed in this paper and results are
presented for the first six galaxies. From a total of 180 HST images,
we provide catalogs of the multi-band stellar photometry and derive
the physical parameters of massive stars by analyzing it with
model-atmosphere colors. We use the results to infer ages, number of
massive stars, extinction, and spatial characteristics of the young
stellar populations. The hot massive star content varies largely
across our galaxy sample, from an inconspicuous presence in Phoenix
and Pegasus to the highest relative abundance of young massive stars
in Sextans A and WLM. Albeit to a largely varying extent, most
galaxies show a very young population (a few Myrs, except for
Phoenix), and older ones (a few 107 years in Sextans A, Sextans B,
NGC 6822, and WLM, ∼108yr in Phoenix and Pegasus), suggesting
discrete bursts of recent star formation in the mapped regions. The
hot massive star content (indicative of the young populations) broadly
correlates with the total galaxy stellar mass represented by the
integrated optical magnitude, although it varies by a factor of ∼3
between Sextans A, WLM, and Sextans B, which have similar MV.
Extinction properties are also derived.
Description:
The star-forming regions were chosen from the Galaxy Evolution
Explorer (GALEX) wide-field far-UV imaging.
Six Local Group galaxies (NGC 6822, Pegasus, Phoenix, Sextans A,
Sextans B, and WLM) were observed with the WFPC2 camera on board the
Hubble Space Telescope (HST) as part of treasury program HST-GO-11079
(PI: L. Bianchi). Imaging in six broadband filters from far-UV to IR
(F170W, F255W, F336W, F439W, F555W, F814W) was acquired at every
pointing to detect and characterize the hot massive star content.
Twelve exposures with each filter were taken at every pointing
yielding a total of 180 images at 15 pointings for these six galaxies,
out of a total of over 800 HST images.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 63 6 The sample Galaxies
table4.dat 166 45203 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/A+A/548/A129 : HST photometry in NGC 6822 (Fusco+, 2012)
J/ApJ/706/599 : Hα and UV SFR in the local volume (Lee+, 2009)
J/ApJS/173/538 : XUV-Disk galaxies in the Local Universe (Thilker+, 2007)
J/ApJS/173/185 : GALEX ultraviolet atlas of nearby galaxies (Gil de Paz+, 2007)
J/AJ/134/2474 : Hα emission-line stars in dwarf galaxies (Massey+, 2007)
J/AJ/131/2478 : M31 and M33 UBVRI photometry (Massey+, 2006)
J/AJ/133/2393 : UBVRI phot. in 7 Local Group dwarfs galaxies (Massey+, 2007)
J/AJ/132/378 : HST and UV photometry of NGC 6822 (Bianchi+, 2006)
J/ApJS/155/1 : Phoenix Deep Survey: optical & NIR catalogs (Sullivan+, 2004)
J/AJ/126/2840 : BVI CCD photometry of Sextans dSph galaxy (Lee+, 2003)
J/AJ/125/1261 : VI photometry of Sextans A Cepheids (Dolphin+, 2003)
J/AJ/121/2020 : CTIO and WFPC2 photometry in NGC 6822 (Bianchi+, 2001)
J/ApJ/521/577 : HST studies of the WLM globular cluster (Hodge+, 1999)
J/AJ/116/2341 : UBVRI photometry in Sextans A (Van Dyk+ 1998)
J/AJ/110/2715 : UBV photometry in NGC 6822, M31 and M33 (Massey+ 1995)
J/A+AS/71/297 : CCD UBV photometry of stars in Sex A (Aparicio+, 1987)
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- 9 A9 --- Gal Galaxy name
11- 14 I4 kpc Dist [406/1370] Estimated distance to each galaxy
16- 18 I3 kpc e_Dist Uncertainty on Dist
20 I1 --- r_Dist Reference for Dist (1)
22- 30 A9 --- MType Galaxy morphological type
32- 35 F4.1 arcmin Maj Isophotal major diameter (25mag/arcsec2^)
36 A1 --- --- [*]
37- 40 F4.1 arcmin min Isophotal minot diameter (25mag/arcsec2^)
42- 46 F5.2 arcmin2 Area1 [5.78/40] Area covered by WFPC2 in arcmin2
48- 51 F4.2 kpc2 Area2 [0.1/2.04] Area covered by WFPC2 in kpc2
53- 57 F5.1 mag VMag [-15.1/-10.1] Absolute visual magnitude
59- 63 F5.1 mag VMag2 [-16.0]? Second absolute visual magnitude
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Note (1): Reference as follows:
1 = Held et al., 1999A&A...345..747H 1999A&A...345..747H
2 = McConnachie et al., 2005MNRAS.356..979M 2005MNRAS.356..979M
3 = Dolphin et al., 2003, Cat. J/AJ/125/1261
4 = Sakai et al., 1997ApJ...480..589S 1997ApJ...480..589S
5 = Gieren et al., 2008ApJ...683..611G 2008ApJ...683..611G
6 = Gieren et al., 2006, Cat. J/ApJ/647/1056
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- Seq [0/26721] Running sequence number
(<[BEH2012] {Gal} NNNNN> in Simbad)
7- 15 A9 --- Gal Parent galaxy name
17- 32 A16 --- IAU Source IAU identifier (JHHMMSS.s-DDMMSS)
34- 44 F11.7 deg RAdeg Right Ascension in decimal degrees (J2000)
46- 56 F11.7 deg DEdeg Declination in decimal degrees (J2000)
58- 62 F5.2 mag F170W [11.99/23.71]?=99 HST/WFPC2 F170W band Vega
magnitude (1)
64- 68 F5.2 mag e_F170W ?=99 Error in F170W
70- 74 F5.2 mag F225W [7.64/23.58]?=99 HST/WFPC2 F225W band Vega
magnitude (1)
76- 80 F5.2 mag e_F225W ?=99 Error in F225W
82- 86 F5.2 mag F336W [11.34/25.96]?=99 HST/WFPC2 F336W band Vega
magnitude (1)
88- 92 F5.2 mag e_F336W ?=99 Error in F336W
94- 98 F5.2 mag F439W [16.31/26.7]?=99 HST/WFPC2 F439W band Vega
magnitude (1)
100-104 F5.2 mag e_F439W ?=99 Error in F439W
106-110 F5.2 mag F555W [16.48/24.59]?=99 HST/WFPC2 F555W band Vega
magnitude (1)
112-116 F5.2 mag e_F555W ?=99 Error in F555W
118-122 F5.2 mag F814W [15.43/23.7]?=99 HST/WFPC2 F814W band Vega
magnitude (1)
124-128 F5.2 mag e_F814W ?=99 Error in F814W
130-134 F5.2 mag Umag [14.77/25.7]?=99 The U band Vega magnitude (1)
136-140 F5.2 mag Bmag [16.28/26.23]?=99 The B band Vega mag. (1)
142-146 F5.2 mag Vmag [16.47/24.57]?=99 The V band Vega mag. (1)
148-152 F5.2 mag Imag [15.39/23.71]?=99 The I band Vega mag. (1)
154-159 F6.3 --- Sharp HSTphot parameters sharpness of the source (1)
161 I1 --- Tp [1/5] HSTphot type of the source, 1=good star (2)
163-164 I2 --- Fr [1/15] The visit number from Table 2 (3)
166 I1 --- Ch [0/3] WFPC2 detector: 0=PC, 1=WF2, 2=WP3, 3=WF4
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Note (1): The UBVI magnitudes were transformed from the F336W, F439W,
F555W, and F814W magnitudes to the Johnson UBVI with HSTphot
(photometry package by Dolphin, A.E. 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 the section 3.4, only
sources with Tp=1 and sharpness between -0.3 and 0.3 should be used
for analysis; sources with any HSTphot type and sharp are included for
completeness.
Note (2): HSTphot types are:
1 = good star;
2 = unresolved binary;
5 = extended objects.
Note (3): HST observations in table 2:
--------------------------------------------------
Galaxy Visit (a) TargetName FileName
--------------------------------------------------
NGC 6822 09 NGC6822-FIELD1 U9WQ09
11 NGC6822-FIELD3 U9WQ11
12 NGC6822-FIELD4 U9WQ12
13 NGC6822-FIELD5 U9WQ13
14 NGC6822-FIELD6 U9WQ14
15 NGC6822-FIELD7 U9WQ15
PEGASUS 08 PEGASUS U9WQ08
PHOENIX 07 PHOENIX U9WQ07
SEXTANSA 05 SEXTANSA-A1+A2 U9WQ05
04 SEXTANSA-A3+A4+A5+A6 U9WQ04
SEXTANSB 06 SEXTANSB U9WQ06
WLM 01 WLM-A1+A3 U9WQ01
02 WLM-A2+A4 U9WQ02
03 WLM-NEW U9WQ03
--------------------------------------------------
(a): Twelve exposures in six filters were taken at
every pointing, with exposure times of 2*600s
in F170W, 300s+260s in F255W, 230s+260s in
F439W, 2*50s in F555W, and 2*60s in F814W.
--------------------------------------------------
History:
From electronic version of the journal
References:
Bianchi et al. Paper II. 2012AJ....144..142B 2012AJ....144..142B Cat. J/AJ/144/142
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 14-May-2013