J/A+A/529/A25 Photometry of star clusters in 5 nearby gal. (Silva-Villa+, 2011)
The star cluster - field star connection in nearby spiral galaxies.
II. Field star and cluster formation histories and their relation.
Silva-Villa E., Larsen S.
<Astron. Astrophys. 529, A25 (2011)>
=2011A&A...529A..25S 2011A&A...529A..25S
ADC_Keywords: Galaxies, nearby ; Associations, stellar ; Photometry, HST
Keywords: galaxies: individual: NGC 5236, NGC 7793, NGC 1313, NGC 45 -
galaxies: star formation - galaxies: photometry
Abstract:
Recent studies have started to cast doubt on the assumption that most
stars are formed in clusters. Observational studies of field stars and
star cluster systems in nearby galaxies can lead to better constraints
on the fraction of stars forming in clusters. Ultimately this may lead
to a better understanding of star formation in galaxies, and galaxy
evolution in general.
We aim to constrain the amount of star formation happening in
long-lived clusters for four galaxies through the homogeneous,
simultaneous study of field stars and star clusters.
Description:
Using HST/ACS and HST/WFPC2 images of the galaxies NGC 45, NGC 1313,
NGC 5236, and NGC 7793, we estimate star formation histories by means
of the synthetic CMD method. Masses and ages of star clusters are
estimated using simple stellar population model fitting. Comparing
observed and modeled luminosity functions, we estimate cluster
formation rates. By randomly sampling the stellar initial mass
function (SIMF), we construct artificial star clusters and quantify
how stochastic effects influence cluster detection, integrated colors,
and age estimates.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table24.dat 74 9 Journal of the observations and 50% completeness
limits for field stars (tables 2 and 4 of the paper)
ngc45.dat 144 80 NGC 45 UBVI photometry
ngc1313.dat 144 815 NGC 1313 UBVI photometry
ngc4395.dat 144 136 NGC 4395 UBVI photometry
ngc5236.dat 144 1407 NGC 5236 UBVI photometry
ngc7793.dat 144 558 NGC 7793 UBVI photometry
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table24.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [NGC]
4- 7 I4 --- NGC Galaxy NGC number
9 I1 --- F Field number
11- 14 I4 s ExpU Exposure time in F336W (U) band
16- 18 I3 s ExpB Exposure time in F435W (B) band
20- 22 I3 s ExpV Exposure time in F555W (V) band
24- 26 I3 s ExpI Exposure time in F814W (I) band
28- 29 I2 h RAh Field right ascension (J2000)
31- 32 I2 min RAm Field right ascension (J2000)
34- 35 I2 s RAs Field right ascension (J2000)
37 A1 --- DE- Field declination sign (J2000)
38- 39 I2 deg DEd Field declination (J2000)
41- 42 I2 arcmin DEm Field declination (J2000)
44- 45 I2 arcsec DEs Field declination (J2000)
47- 56 A10 "YYYY.MM.DD" Date Observation date
58- 62 F5.2 mag Bmaglim 50% completeness limit for F435W(B) band
64- 68 F5.2 mag Vmaglim 50% completeness limit for F555W(V) band
70- 74 F5.2 mag Imaglim 50% completeness limit for F814W(I) band
--------------------------------------------------------------------------------
Byte-by-byte Description of file: ngc*.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [NGC]
4- 7 I4 --- NGC Parent Galaxy NGC number
8 A1 --- --- [_]
9- 13 A5 --- Cl Cluster identification, as F_NNN (field-number)
15- 19 I5 --- ID ID photometry number
21- 25 I5 pix Xpos X coordinate over ACS
27- 31 I5 pix Ypos Y coordinate over ACS
33- 34 I2 h RAh Right ascension (J2000)
36- 37 I2 min RAm Right ascension (J2000)
39- 43 F5.2 s RAs Right ascension (J2000)
45 A1 --- DE- Declination sign (J2000)
46- 47 I2 deg DEd Declination (J2000)
49- 50 I2 arcmin DEm Declination (J2000)
52- 56 F5.2 arcsec DEs Declination (J2000)
59- 63 F5.2 mag Umag ?=0 HST F336W (U-band) magnitude
66- 70 F5.2 mag e_Umag ?=0 U magnitude error
73- 77 F5.2 mag Bmag ?=0 HST F435W (B-band) magnitude
81- 84 F4.2 mag e_Bmag ?=0 B magnitude error
87- 91 F5.2 mag Vmag ?=0 HST F555W (V-band) magnitude
95- 98 F4.2 mag e_Vmag ?=0 V magnitude error
101-105 F5.2 mag Imag ?=0 I magnitude
108-112 F5.2 mag e_Imag ?=0 HST F814W (I-band) magnitude error
115-119 F5.2 [yr] log(age) ?=0 Logarithm of clusters age,
estimated for LMC-like metallicity
122-126 F5.2 [Msun] log(M) ?=0 Logarithm of clusters mass,
estimated for LMC-like metallicity
127-132 F6.2 pix FWHM-S FWHM size measured with SExtractor
134-138 F5.2 pix FWHM-I FWHM size measured with Ishape
141-144 A4 --- flag [acpt susp] Flag for accepted and suspected
objects
--------------------------------------------------------------------------------
Acknowledgements:
Esteban Silva Villa, e.silvavilla(at)uu.nl
(End) Patricia Vannier [CDS] 22-Mar-2011