J/A+A/533/A91 Deep VI imaging in outer regions of M33 (Grossi+, 2011)
Stellar structures in the outer regions of M33.
Grossi M., Hwang N., Corbelli E., Giovanard C., Okamoto S., Arimoto N.
<Astron. Astrophys. 533, A91 (2011)>
=2011A&A...533A..91G 2011A&A...533A..91G
ADC_Keywords: Galaxies, nearby ; Galaxies, photometry ; Photometry, CCD
Keywords: galaxies: evolution - galaxies: stellar content - galaxies: halos -
galaxies: individual: M33
Abstract:
We present Subaru/Suprime-Cam deep V and I imaging of seven fields in
the outer regions of M33. Our aim is to search for stellar structures
corresponding to extended HI clouds found in a recent 21-cm survey of
the galaxy. Three fields probe a large HI complex to the southeastern
(SE) side of the galaxy. An additional three fields cover the
northwestern (NW) side of the galaxy along the HI warp. A final target
field was chosen further north, at a projected distance of
approximately 25kpc, to study part of the large stellar plume
recently discovered around M33.
We analyse the stellar population at R>10kpc by means of V, I
colour magnitude diagrams reaching the red clump. We constrain the age
and metallicity of the different stellar populations, search for
density enhancements that correspond to the HI features, and
investigate the radial surface distribution of the stars.
We find evolved stellar populations in all fields out to 120'
(∼30kpc), while a diffuse population of young stars (∼200Myr) is
detected out to a galactocentric radius of 15kpc. The mean metallicity
in the southern fields remains approximately constant at [M/H]=-0.7
beyond the edge of the optical disc, from 40' out to 80'. Along the
northern fields probing the outer HI disc, we also find a metallicity
of [M/H]=-0.7 between 35' and 70' from the centre, which decreases to
[M/H]=-1.0 at larger angular radii out to 120'. In the northernmost
field, outside the disc extent, the stellar population of the large
stellar plume possibly related to a M33-M31 interaction is on average
more metal-poor ([M/H]=-1.3) and older (>6Gyr).
An exponential disc with a large scale-length (∼7kpc) fits well the
average distribution of stars detected in both the SE and NW regions
from a galactocentric distance of 11kpc out to 30kpc. The stellar
disc extends beyond the HI disc. The stellar distribution at large
radii is disturbed and, although there is no clear correlation between
the stellar substructures and the location of the HI clouds, this
gives evidence of tidal interaction or accretion events.
Description:
V,I stellar photometry in seven fields in the outer regions of M33
corresponding to extended neutral hydrogen clouds found in a recent
21-cm survey of the galaxy. The fields are named as SE1, SE2, SE3,
NW4, NW5, NW6, NW7. An additional field named BG at approximately four
degrees to the east of the optical centre of M33 was selected to
inspect the contamination from background and foreground sources. For
each field X, Y position in the V and I frames, equatorial
coordinates, V, I magnitudes and corresponding errors are given. The
colour magnitude diagrams obtained with this photometry are shown in
Figures 2, 3 and 4.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 51 8 Central coordinates of the target fields observed
with Subaru/Suprime-Cam
bg.dat 99 4605 Star positions and magnitudes in field BG
nw4.dat 99 4357 Star positions and magnitudes in field NW4
nw5.dat 99 3681 Star positions and magnitudes in field NW5
nw6.dat 99 2749 Star positions and magnitudes in field NW6
nw7.dat 99 3762 Star positions and magnitudes in field NW7
se1.dat 99 2345 Star positions and magnitudes in field SE1
se2.dat 99 2260 Star positions and magnitudes in field SE2
se3.dat 99 8554 *Star positions and magnitudes in field SE3
--------------------------------------------------------------------------------
Note on se3.dat: In Figure 2 of the paper, the colour magnitude diagrams
obtained from field SE3 -- SE3a, SE3b -- are related to stars to the
East and West of RA=24.215°, respectively.
--------------------------------------------------------------------------------
See also:
J/AJ/110/2739 : H-alpha emitting regions in M33 (Calzetti+ 1995)
J/A+A/366/498 : VI photometry of M33 star clusters (Chandar+, 2001)
J/A+A/426/11 : XMM-Newton survey of M33 (Pietsch+, 2004)
J/A+A/476/1161 : Spitzer photometry of M33 (Verley+, 2007)
J/ApJ/664/850 : Spitzer observations of stars in M33 (McQuinn+, 2007)
J/AJ/128/224 : VI photometry in M33 outer regions (Tiede+, 2004)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Fld Field designation
5- 6 I2 h RAh Right ascension (J2000)
8- 9 I2 min RAm Right ascension (J2000)
11- 14 F4.1 s RAs Right ascension (J2000)
16 A1 --- DE- Declination sign (J2000)
17- 18 I2 deg DEd Declination (J2000)
20- 21 I2 arcmin DEm Declination (J2000)
23- 24 I2 arcsec DEs Declination (J2000)
26- 29 F4.1 kpc r ?=- Corresponding projected distance from M33
(for distance(M33) = 840 kpc)
31- 33 F3.1 arcsec Vsee Seeing in V image
34 A1 --- --- [/]
35- 37 F3.1 arcsec Isee Seeing in I image
39- 43 F5.3 mag AV Extinction value adopted for the field
45- 51 A7 --- FileName Name of the file with field photometry
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): bg.dat nw*.dat se*.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.2 pix Vxpos X coordinate on V frame
12- 19 F8.2 pix Vypos Y coordinate on V frame
23- 30 F8.2 pix Ixpos X coordinate on I frame
34- 41 F8.2 pix Iypos Y coordinate on I frame
45- 53 F9.6 deg RAdeg Right ascension (J2000.0)
57- 65 F9.6 deg DEdeg Declination (J2000.0)
69- 74 F6.3 mag Vmag V magnitude (1)
78- 82 F5.3 mag e_Vmag Error on V magnitude
86- 91 F6.3 mag Imag I magnitude (1)
95- 99 F5.3 mag e_Imag Error on I magnitude
--------------------------------------------------------------------------------
Note (1): Correction for foreground Galactic extinction according to Schlegel
et al. (1998ApJ...500..525S 1998ApJ...500..525S) corresponds to the centre of the field.
--------------------------------------------------------------------------------
Acknowledgements:
Marco Grossi, grossi(at)oal.ul.pt
(End) Marco Grossi [CAAUL, Portugal], Patricia Vannier [CDS] 06-Sep-2011