J/A+A/335/85 HST photometry of ESO 338-IG04 globular clusters (Oestlin+, 1998)
Globular clusters in the blue compact galaxy ESO 338-IG04 (Tololo 1924-416), as
tracers of the star formation history. Results from HST/WFPC2 observations.
Oestlin G., Bergvall N., Roennback J.
<Astron. Astrophys. 335, 85 (1998)>
=1998A&A...335...85O 1998A&A...335...85O
ADC_Keywords: Clusters, globular ; Photometry
Keywords: galaxies: compact - galaxies: starburst - galaxies: star clusters -
galaxies: evolution - galaxies: interaction -
galaxies: individual: ESO 338-IG04 = Tol 1924-416
Abstract:
Multicolour images of the starbursting metal poor blue compact galaxy
ESO 338-IG04 have been obtained with the Wide Field Planetary Camera 2
on board the Hubble Space Telescope. In the images we find numerous
point-like sources concentrated towards the main body of the galaxy,
which we identify as globular cluster candidates. We show that these
objects are physically associated with the galaxy and that they are
spatially extended. Given their high intrinsic luminosities, these
objects cannot be individual stars. Using photometric evolution models
we show that the objects constitute a rich population of massive star
clusters with ages ranging from a few Myr to 10Gyr, and masses
ranging from 104 to more than 107M☉. There are peaks in the
age distribution of the clusters: one with objects ≤30Myr, one at
∼100Myr, one at ∼600Myr, one to two at 2.5-5Gyr and one at ∼10Gyr.
The youngest objects are predominantly found in the crowded starburst
region. They have properties which agree with what is expected for
young globular clusters, although it cannot be excluded that some of
them may be dissolved or disrupted. For objects older than a few times
10Myr, the only plausible explanation is that these are globular
clusters. The galaxy presently appears to be involved in a merger,
which is the probable cause of the present globular cluster formation.
The presence of a numerous intermediate age (2.5 to 5Gyr) population
of globular clusters, suggests that a previous merger might have
occurred. As the starburst fades, this galaxy will become very rich in
globular clusters. Transforming all objects to an age comparable to
that of Milky Way globular clusters reveals a luminosity function
similar to the Galactic. We suggest that this galaxy is the result of
a merger between a dwarf elliptical and a gas rich dwarf. The
possibility of dating the globular clusters offers an efficient way of
studying the history of violent star formation in this and similar
galaxies.
Objects:
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RA (2000) DE Designation(s)
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19 27 58.1 -41 34 27 Tol 1924-416 = ESO 338- 4
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 87 64 Photometry of object in the outer sample with
m814 < 24
table2.dat 87 60 Photometry of object in the inner sample with
m814 < 23.5
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Byte-by-byte Description of file: table1.dat table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- [OBR98] Sequential number (1)
3- 5 A3 --- n_[OBR98] [* ] Note (2)
7- 11 F5.1 pix Xpos X position (3)
13- 17 F5.1 pix Ypos Y position (3)
19- 23 F5.2 mag m814 F814W magnitude (4)
25- 28 F4.2 mag e_m814 rms uncertainty on m814
30- 34 F5.2 mag m555 ? F555W magnitude (4)
36- 39 F4.2 mag e_m555 ? rms uncertainty on m555
41- 45 F5.2 mag m439 ? F439W magnitude (4)
47- 50 F4.2 mag e_m439 ? rms uncertainty on m439
52- 56 F5.2 mag m336 ? F336W magnitude (4)
58- 61 F4.2 mag e_m336 ? rms uncertainty on m336
63- 67 F5.1 mag vMAG Absolute v magnitude (or i if n_VMAG ='*')
68 A1 --- n_vMAG [*] * when absolute i magnitude in VMAG
70 A1 --- l_v-i Limit flag on v-i
71- 75 F5.2 mag v-i v-i colour index
77- 81 F5.2 mag b-v ? b-v colour index
83- 87 F5.2 mag u-b ? u-b colour index
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Note (1): Table 1: [OBR98] outer NN, in Simbad
Table 2: [OBR98] inner NN, in Simbad
Note (2): Note:
**: probable background galaxy/foreground star
***: possible background galaxy/foreground star
Note (3): The field of ESO 338-IG04 was observed with the PC aperture,
centred on RA = 19h 28min 00.23s (2000) DE = -41° 34' 21.2".
The pixel scale of the PC CCD is 0.0455 arcseconds, which at a
distance of 37.5 Mpc corresponds to 8.27 pc.
North is up and east is left.
Note (4): Magnitudes refer to the photometric zero-points for Vega.
The data have been corrected for Galaic reddening.
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History:
Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 25-Jun-2001