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
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 (# headlines): 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) 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
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