J/A+A/572/A26 HST photometry in NGC 6822 (Fusco+, 2014)
A state-of-the-art analysis of the dwarf irregular galaxy NGC 6822.
Fusco F., Buonanno R., Hidalgo S.L., Aparicio A., Pietrinferni A., Bono G.,
Monelli M., Cassisi S.
<Astron. Astrophys. 572, A26 (2014)>
=2014A&A...572A..26F 2014A&A...572A..26F
ADC_Keywords: Galaxies, photometry ; Photometry, HST ; Stars, distances
Keywords: galaxies: individual: NGC 6822 - Local Group - galaxies: dwarf -
galaxies: star formation
Abstract:
We present a detailed photometric study of the dwarf irregular galaxy
NGC 6822 aimed at investigating the properties of its stellar
populations, and in particular, the presence of stellar radial
gradients. Our goal is to analyze the stellar populations in six
fields, which cover the whole bar of this dwarf galaxy. We derived the
quantitative star formation history (SFH) of the six fields using the
IAC method, involving IAC-pop/MinnIAC codes. The solutions we derived
show an enhanced star formation rate (SFR) in fields 1 and 3 during
the last 500Myr. The SFRs of the other fields almost extinguish at
very recent epochs. We study the radial gradients of the SFR. We
consider the total mass converted into stars in two time intervals
(between 0 and 0.5Gyr ago and between 0.5 and 13.5Gyr ago). We find
that the scale lengths of the young and intermediate-old populations
are perfectly compatible, with the exception of the young populations
in fields 1 and 3. The recent SF in these two fields is larger than in
the other ones. This might be an indication that in these two fields
we are sampling incipient spiral arms. Further evidence and new
observations are required to prove this hypothesis. In addition, we
derived the age-metallicity relations. As expected, for all of the
fields the metallicity increases with time. We do not observe any
radial gradient in the metallicity.
Description:
We performed HST photometry on three fields in the north-west region
of NGC 6822 galaxy. The resulting catalogues contain ∼14,000, ∼3,500,
∼3,800 stars, from the innermost to the outermost field. Data were
calibrated using the VEGAMAG system. Data are stored in three files,
one for each field: central field (n6822_3.dat),
middle field (n6822_2.dat) and outer field (n6822_1.dat).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
n6822_1.dat 123 3740 Photometric catalogue in F475W and F814W
HST bands for the outermost field
n6822_2.dat 123 3530 Photometric catalogue in F475W and F814W
HST bands for the middle field
n6822_3.dat 123 13423 Photometric catalogue in F475W and F814W
HST bands for the innermost field
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See also:
J/AJ/121/2020 : CTIO and WFPC2 photometry in NGC 6822 (Bianchi+, 2001)
J/A+A/429/837 : NGC 6822 late-type stars IJKs photometry (Cioni+, 2005)
J/A+A/454/717 : NGC 6822 C and AGB stars near-IR photometry (Kang+, 2006)
J/A+A/456/905 : NGC 6822 C stars JKs, i'g'r' photometry (Demers+, 2006)
J/AJ/132/378 : HST and UV photometry of NGC 6822 (Bianchi+, 2006)
J/AJ/132/1372 : Chandra observation of NGC 6822 (Tennant+, 2006)
J/A+A/537/A108 : NGC 6822 AGB spectroscopic catalogue (Kacharov+, 2012)
J/ApJ/730/88 : NGC 6822 star-forming regions from UV data (Efremova+, 2011)
J/A+A/540/A135 : AGB population of NGC 6822 (Sibbons+, 2012)
J/A+A/548/A129 : HST photometry in NGC 6822 (Fusco+, 2012)
J/MNRAS/428/2216 : JHKs photometry of AGB stars in NGC 6822 (Whitelock+, 2013)
Byte-by-byte Description of file: n6822_1.dat n6822_2.dat n6822_3.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- ID [1/13423] Star identification number
8- 15 F8.3 pix Xpos [0/4096] X coordinate in pixels
17- 24 F8.3 pix Ypos [0/4096] Y coordinate in pixels
28- 33 F6.3 mag F475W [18.3/30.5] HST/ACS F475W Vega magnitude
37- 42 F6.4 mag e_F475W Error associated to F475W magnitude
46- 51 F6.3 mag F814W [16.7/58.9] HST/ACS F814W Vega magnitude
55- 60 F6.4 mag e_F814W Error associated to F814W magnitude
63- 69 F7.4 --- chi [1/50] Mean value of the χ image-quality
DAOPHOT index (close to 1 is good)
72- 78 F7.4 --- Sharp [-5/15] Mean value of the sharp image-quality
index (stars with |Sharp|≤0.5 were considered)
82- 83 I2 h RAh Right ascension (J2000)
87- 88 I2 min RAm Right ascension (J2000)
91- 97 F7.4 sec RAs Right ascension (J2000)
101 A1 --- DE- Declination sign (J2000)
102-103 I2 deg DEd Declination (J2000)
108-109 I2 arcmin DEm Declination (J2000)
113-118 F6.3 arcsec DEs Declination (J2000)
123 I1 --- Chip [1/2] Chip number of the camera (1=WFC1, 2=WFC2)
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Acknowledgements:
Federica Fusco, federica.fusco(at)roma2.infn.it
(End) F. Fusco [Univ. of Rome Tor Vergata, Italy], P. Vannier [CDS] 09-Sep-2014