J/A+A/443/41 NGC 4038/4039 broad and /narrow band photometry (Mengel+, 2005)
Star-formation in NGC 4038/4039 from broad- and narrow band photometry:
Cluster Destruction?
Mengel S., Lehnert M.D., Thatte N., Genzel R.
<Astron. Astrophys. 443, 41 (2005)>
=2005A&A...443...41M 2005A&A...443...41M
ADC_Keywords: Associations, stellar ; Photometry
Keywords: galaxies: star clusters - galaxies: individual: NGC 4038/4039 -
galaxies: interaction
Description:
The Ks-band image which was used for the 3σ-detection was
obtained with ISAAC on VLT-ANTU as part of programme 65.N-0577, and
has a FWHM of ∼0.38". 1072 point-like objects were detected. For the
multi-band photometry, we also used the HST archival images obtained
by Whitmore et al. (see Whitmore et al., 1999AJ....118.1551W 1999AJ....118.1551W), which
we rebinned to the same pixel size as the ISAAC image (0.1484"/pix).
The CO narrow band image was also obtained with ISAAC, while the
Brγ image was obtained with SOFI at the NTT (programme number
63.N-0528). The Brγ image had a lower image quality than the
other two images (FWHM=0.7"). The photometry data were used to
simultaneously fit age and extinction for each individual cluster in
comparison to an evolutionary synthesis model. Where possible, the
visual extinction was determined from an average of the extinction
from the broadband fit and from the Hydrogen recombination line ratios
(in comparison to the expected Case B line ratio). The age estimate
from the fit was, where possible, averaged with the aged determined
from equivalent widths and CO index.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 104 1072 Broad- and narrow-band photometry
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See also:
J/AJ/109/960 : Young star clusters in The Antennae (Whitmore+ 1995)
J/AJ/124/1418 : Radio-optical identification of star clusters (Whitmore+ 2002)
J/AJ/127/660 : Photometry in southern tail of the Antennae (Saviane+, 2004)
J/ApJ/561/727 : BVI photometry in the Antennae galaxies (Zhang+, 2001)
J/ApJ/599/1049 : Supergiant molecular complexes in the Antennae (Wilson+, 2003)
Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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1- 6 F6.2 arcsec dRA Distance in RA to RA = 12 01 52.97 (1)
8- 13 F6.2 arcsec dDE Distance in DE to DE = -18 52 08.29 (1)
15- 19 F5.2 mag Umag ? Apparent Johnson U magnitude (2)
21- 25 F5.2 mag Bmag ? Apparent Johnson B magnitude (2)
27- 31 F5.2 mag Vmag ? Apparent Johnson V magnitude (2)
33- 37 F5.2 mag Imag ? Apparent Cousins I magnitude (2)
39- 43 F5.2 mag Ksmag Apparent Ks magnitude (2)
45- 51 F7.2 0.1nm EWHa ? Equivalent width of Hα (3)
53- 58 F6.2 0.1nm EWBrg ? Equivalent width of Brγ (4)
60- 64 F5.2 mag COindex ? CO index (5)
66- 70 F5.2 mag AV ? Visual extinction (6)
72- 77 F6.2 Myr Age Age (7)
79- 81 F3.1 --- q_Age Quality of the age estimate (8)
83- 88 F6.2 10+5solMass Massph Photometric mass (9)
90- 94 F5.1 pix Dist Distance to nearest cluster (10)
96-105 A10 --- Cross-ID Cross-Identification (11)
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Note (1): The reference position (deltaRA, deltaDec = 0,0) we are using
is the same as that used in Whitmore et al., 1999AJ....118.1551W 1999AJ....118.1551W,
namely: RA = 12 01 52.97, DE = -18 52 08.29 (J2000)
Note (2): Magnitudes are not extinction corrected. Aperture correction
using a fixed value (0.7(0.5)mag for V(Ks)) from a fixed aperture
(5(3)pix for V(Ks)) was applied if the closest neighbour was closer
than 10(12) pixels (for V(Ks) band) (see column 15). For isolated
clusters, the total apparent cluster magnitude was determined by a
curve-of-growth technique. Only the magnitudes for V and Ks-band were
determined directly. U, B, and I magnitudes were determined from the
difference to the V band in an aperture of r=3pix.
Note (3): The continuum flux was determined from an interpolation of the
V and the I band for the wavelength of Halpha in NGC 4038/4039. The
equivalent width was determined from a small aperture (r=3pix) which,
for clusters with extended shells, underestimates the total Hα
flux.
Note (4): The Brγ SOFI image had a lower image quality than the
Ks-band ISAAC image. In order to determine the continuum flux for
a given cluster, the Ks-image was degraded to a comparable FWHM
(0.7" for the SOFI image, as opposed to 0.38" for the ISAAC image).
Note (5): We constructed our CO index from the difference in magnitudes
(for an aperture with r=5pix) between the ESO CO2.34 narrow band
filter and the Ks filter. This value is not extinction corrected.
Note (6): Visual foreground screen extinction. Determined, where
applicable, from an average of the extinction determined from the
broadband fit and the extinction from the line ratios.
Note (7): Age determined in comparison to the Starburst99 evolutionary
synthesis model (Leitherer et al., 1999ApJS..123....3L 1999ApJS..123....3L), for an
instantaneous burst, solar metallicity, Salpeter IMF between 1 and
100M☉. The value reported in this column is, where possible,
an average of the four age indicators that may be present: Fit to
the broadband colours, WHa, WBrg and COindex. See also the column
q_Age for the reliability of the age estimate.
Note (8): This (arbitrary value) parameter indicates the quality of the
age determination. The higher the number (4.0 being highest), the more
reliable the assigned cluster age. 3.0 and higher show reasonable to
good agreement, 1.5 and lower show severe disagreement in at least one
age indicator and should be treated with caution (they were excluded
from the analysis in the paper).
Note (9): Photometric mass of the cluster, determined from the extinction
corrected K-band magnitude, in combination with the age. Note the
model assumptions which influence this value quoted in Note (7),
particularly IMF slope and mass cutoffs.
Note (10): Distance in pixels to the nearest cluster which was also detected
in Ks-band. This parameter is used for the decision which method to
use to determine the total magnitude of the cluster (see Note (2)).
Note (11): Cross-identification of a few clusters and stars with objects
listed in Whitmore et al., 1999AJ....118.1551W 1999AJ....118.1551W (W99, W99-N = [WZL99]
1- N, W99-StarN = [WZL99] 4- N in Simbad) and in Whitmore & Schweizer,
1995, Cat. J/AJ/109/960 (WS95, [WS95] NNN in Simbad). Magnitudes
differ for some objects, most likely due to different aperture
corrections (see also detailed analysis of surface brightness profiles
for three clusters in W99, Sec. 4.4.2).
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Acknowledgements: Sabine Mengel, smengel(at)eso.org
(End) Patricia Vannier [CDS] 02-Jun-2005