J/AJ/144/182 Stellar groups in IC 2574 (Pellerin+, 2012)
Hunting for young dispersing star clusters in IC 2574.
Pellerin A., Meyer M.M., Calzetti D., Harris J.
<Astron. J., 144, 182 (2012)>
=2012AJ....144..182P 2012AJ....144..182P
ADC_Keywords: Associations, stellar ; Stars, ages
Keywords: galaxies: individual: IC 2574 - galaxies: star clusters: general -
galaxies: stellar content - stars: early-type
Abstract:
Dissolving stellar groups are very difficult to detect using
traditional surface photometry techniques. We have developed a method
to find and characterize non-compact stellar systems in galaxies where
the young stellar population can be spatially resolved. By carrying
out photometry on individual stars, we are able to separate the
luminous blue stellar population from the star field background. The
locations of these stars are used to identify groups by applying the
HOP algorithm, which are then characterized using color-magnitude and
stellar density radial profiles to estimate age, size, density, and
shape. We test the method on Hubble Space Telescope Advanced Camera
for Surveys archival images of IC 2574 and find 75 dispersed stellar
groups. Of these, 20 highly dispersed groups are good candidates for
dissolving systems. We find few compact systems with evidence of
dissolution, potentially indicating that star formation in this galaxy
occurs mostly in unbound clusters or groups. These systems indicate
that the dispersion rate of groups and clusters in IC 2574 is at most
0.45pc/Myr. The location of the groups found with HOP correlate well
with HI contour map features. However, they do not coincide with HI
holes, suggesting that those holes were not created by star-forming
regions.
Description:
Archival images from the Advanced Camera for Surveys (ACS) on board
the Hubble Space Telescope (HST) were downloaded from the Multimission
Archive at STScI (MAST, http://archive.stsci.edu/). Observations were
originally taken on 2004 February 6 for the cycle 12 project ID 9755
(PI: F. Walter) in the F435W, F555W, F814W, and F658N filters (roughly
B, V, I, and Hα). The field of view includes the SuperGiant
Shell (SGS) and its triggered star formation sites, as well as another
strong HII region.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 83 27 Physical properties of stellar groups wit
nebular emission (category I)
table3.dat 83 28 Physical properties of stellar groups found
with HOP (category II)
table4.dat 83 20 Physical properties of highly dispersed stellar
groups (category III)
notes.dat 762 75 Notes
--------------------------------------------------------------------------------
See also:
VII/161 : Nearby Galaxies (Schmidt+ 1993)
J/ApJ/744/44 : Hα and UV fluxes in nearby galaxies (Weisz+, 2012)
J/MNRAS/412/1539 : Ages of stars in dwarf galaxies (Bastian+, 2011)
J/ApJ/733/87 : Star formation efficiency in galaxies (Shi+, 2011)
J/ApJ/734/L22 : ACS Nearby Galaxy Survey Treasury (Williams+, 2011)
J/ApJS/192/10 : Chandra ACIS survey in 383 nearby galaxies. I. (Liu, 2011)
J/ApJ/714/1256 : Far-IR star formation rate indicators (Calzetti+, 2010)
J/ApJS/190/147 : Mid-IR galaxy morphology from S4G (Buta+, 2010)
J/PASP/122/1397 : Spitzer Survey of Stellar Structure in Gal. (Sheth+, 2010)
J/ApJS/190/233 : Spectroscopy & abundances of SINGS gal. (Moustakas+, 2010)
J/ApJ/701/1965 : Radial dust properties of SINGS gal. (Munoz-Mateos+, 2009)
J/ApJ/706/516 : Gas content of star-forming gal. (Pflamm-Altenburg+, 2009)
J/ApJ/703/517 : The Spitzer Local Volume Legacy: IR photometry (Dale+, 2009)
J/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)
J/ApJS/173/185 : GALEX UV atlas of nearby galaxies (Gil de Paz+, 2007)
J/AJ/120/1794 : Far-UV observations of the shell in IC 2574 (Stewart+, 2000)
J/other/Ap/41.1 : Catalog of barred galaxies (Kandalian+, 1998)
http://archive.stsci.edu/ : MAST Web site
Byte-by-byte Description of file: table[234].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Name Dispersed stellar group identifier
(<[PMC2012] NNa> in Simbad)
5- 8 I4 pix Xpos x coordinate in the pixel map (see Figure 4)
10- 13 I4 pix Ypos y coordinate in the pixel map (see Figure 4)
15- 16 I2 h RAh Hour of Right Ascension (J2000)
18- 19 I2 min RAm Minute of Right Ascension (J2000)
21- 26 F6.3 s RAs Second of Right Ascension (J2000)
28 A1 --- DE- Sign of the Declination (J2000)
29- 30 I2 deg DEd Degree of Declination (J2000)
32- 33 I2 arcmin DEm Arcminute of Declination (J2000)
35- 39 F5.2 arcsec DEs Arcsecond of Declination (J2000)
41- 45 F5.3 --- Ell [0/1] Ellipticity ε
47- 50 I4 deg PA [-115/200] Position angle
56- 58 I3 pc Size Size
60 A1 --- n_Size [-?] - when interval, ? for other possible value
62- 64 I3 pc Size1 ? Upper limit on Size if interval
66- 70 F5.3 pc-2 N Star number density (in units of stars/pc-2)
72- 73 A2 --- l_Age [?~≤ ] Uncertainty or upper limit flag on Age
75- 77 I3 Myr Age Cluster age (1)
79 A1 --- f_Age [-,] Flag for interval (-),
or alternative value (,) (2)
81- 83 I3 Myr Age1 ? Upper limit if interval or second value of Age
--------------------------------------------------------------------------------
Note (1): Rough estimates based on the CMDs and Padova isochrones.
Note (2): Flag means the following:
- = when interval;
, = The stellar group 02z is a large and fairly dispersed young group with
faint nebular emission. The CMD suggests a dual population, one with
several evolved red stars of ∼30-40Myr plus another younger one of ∼10Myr.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: notes.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Name Dispersed stellar group identifier
5-762 A758 --- Note Notes
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Sylvain Guehenneux [CDS] 09-Jan-2014