DEEP MULTICOLOR NIR SURVEY OF THE
GALACTIC PLANE
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gotzon
18-1-95
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A. Cabrera-Lavers , F. Garzón , P. L. Hammersley , B. Vicente and C. González
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(1) Instituto de Astrofísica de Canarias, Tenerife, Spain (2) Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain
Comparison with other NIR surveys
ABSTRACT
We present a deep multicolor NIR survey that we are currently
building at the Instituto de Astrofisica de Canarias using the 2D NIR
camera CAIN at the 1.5m Carlos Sanchez Telescope. The aim of the
survey is obtain deep star counts in some selected areas to analyze
the large scale structure of the Milky Way and some galactic
components, in particular the Galactic bar. We get more than one
magnitude deeper than in 2MASS and DENIS galactic surveys, and
even more in the inner Galaxy, as we are less limited by source
confusion effects, providing a better analysis of those regions where
the extinction is higher.
The Two Micron All Sky Survey (2MASS) and the Deep Near Infrared
Survey of the Southern Sky (DENIS) are the largest NIR Galactic surveys in
area covered that we can use nowadays. TCS-CAIN survey cannot be
compared with those ones in terms of spatial coverage, as we obtain point
sources detection in regions of 0.07 deg2 in the sky. However, as a
combination of a smaller pixel size and larger integration times we can
provide deeper photometry, being less afected by source confussion.
Cross-correlations between DENIS and 2MASS respect to TCS-CAIN
survey have been done in several fields showing that mean photometric
differences are less than 0.2 mag for the filters in common, and less than
0.3" in the astrometric measurements.
Near Infrared Galactic surveys
Figure 1: Images of l=27o b=0o taken from 2MASS (left) and TCS-CAIN
(right). The smaller pixel size cause the TCS-CAIN survey being less
afected by source confusion.
Star counts have been used for years to examine the stellar contents in the
Galaxy (see Paul 1993), whose structural parameters of the various
morphological components are still far from being completely known. In the
last two decades there has been a combined effort in this topic with the use
of detailed models of stellar galactic distribution along with large area, high
sensitivity and multicolor star counts surveys. The near infrared (NIR)
members of these surveys (Garzón et al. 1993, Epchtein 1997, Skrutskie et
al. 1997) are notably useful for the analysis of the galactic structure
because of smaller interstellar extinction compared with the optical bands,
in particular in the hidden in plane areas in the inner Galaxy. It is in this
zones where the morphological structures are less studied and where we
have emphasized our observational effort with the multicolor survey we are
presenting here.
Observation technique
Observations have been made using CAIN, the facility IR camera on the
1.5m Telescopio Carlos Sánchez (TCS) (Observatorio del Teide, Tenerife).
Sky is being scanned in series of 20x12 arcmin2 divided in a grid of 3x5
frames around the selected central position. The field of view of CAIN is 4´x
4´with a plate scale of 1"/pix, and with overlaps of 20" between adjacent
frames. Telescope pointings are mainly distributed along the Galactic
Plane or not very far from it (|b|<5o), as one of the purposes of the survey is
characterizing the stellar content of the Galactic disc. Typical exposure
times are 15 sec both in the J and H bands, and 16 sec in the K band. With
those integration times, limiting magnitudes are 17, 16,5 and 15.2 in J,H,
and Ks respectively. There is also a serie of observations where the
exposure times were increased by a factor 5 with the aim of obtainig deeper
photometry in some specific areas of the sky, getting more than 1.2 mags
deeper than the nominal survey in the outer galactic disc (l>45o).
Filter
J
H
Ks
Zero-point (mag)
21.184±0.035
21.041±0.033
20.272±0.033
-1
Kl(mag airmass )
0.188±0.012
0.156±0.014
0.168±0.015
Table 1: Mean transformation coefficients for the TCS-CAIN survey.
Data have been collected and reduced at the IAC for aproximately 600
fields to date, with more than 10 million of point sources detected.
Photometry has been done using standar IRAF DAOPHOT package, with
corrections from analytic PSFs before extracting final magnitudes.
Calibration to the standard system has been done by using Faint Stars
standards (FS) from the UKIRT catalog.
Figure 2: Comparison between K/J-K color-magnitude diagrams in l=27o b=0o obtained with 2MASS (left), TCS-CAIN (center) and DENIS
(right). The clump around J-K=1.8, K=12.5 has been identified as the end of the Galactic Bar (Hammersley et al. 2000). As shown, TCS-CAIN
survey is 2 mags deeper than 2MASS and DENIS in the K band, providing a better analysis of the galactic structure in this region.
250
Implications in Galactic structure
200
At present, TCS-CAIN data have been used in differents ways of analyzing
the large scale Galactic structure. Excess in the K-band star counts
obtained on the Galactic Plane around l=27o was a first indicator of the
existence of a Galactic Bar (Hammersley et al. 2000). NIR CMDs obtained
with TCS-CAIN data have been used in developing an empirical method to
obtain both the interstellar extinction and the stellar density along a selected
line of sight by extracting the K2IIII population from the CMDs (LópezCorredoira et al. 2002, Picaud et al. 2003).
150
100
50
0
0
50
100
150
x(")
200
250
0.1 "
Figure 3: (Left) Distortion pattern for the CAIN camera, that is corrected
during the astrometric reduction. (Right) Internal astrometric differences of
TCS-CAIN obtained by comparising objects lying in overlapped frames.
References
* Epchtein, N. 1997, in The Impact of Large Scale Near-IR Surveys, F.
Garzón, N. Epchtein, A. Omont, B. Burton, P. Persi, eds., Kluwer, Dordrecht,
p. 451.
* Garzón, F. Hammersley, P.L., Mahoney, T., et al. 1993, MNRAS, 264, 773.
* Hammersley, P.L., Garzón, F., Mahoney, T., et al. 2000, MNRAS, 317, L45.
* López-Corredoira, M., Cabrera-Lavers, A., Garzón, F., Hammersley, P.L.,
2002, A&A, 394, 883.
* Paul, E.R., 1993, in The Milky Way Galaxy and Statistical Cosmology,
1890-1924 (Cambridge University Press, Cambridge).
* Picaud, S., Cabrera-Lavers, A., Garzón, F., 2003, A&A, 408, 141.
* Skrutskie, M.F., et al. 1997, in The Impact of Large Scale Near-IR Surveys,
F. Garzón, N. Epchtein, A. Omont, B. Burton, P. Persi, eds., Kluwer,
Dordrecht, p. 25.
Figure 4: Star counts in the plane by combinig data from 2MASS and
TCS-CAIN. Solid line is the prediction of a disc model that includes the
effect of a flare and a warp in the stellar distribution (López-Correodoira
et al. 2002). We observe that TCS-CAIN counts fit well within the
predictions of the model and that the 2MASS counts up to mK=15 lie
below the model, due to effects of completeness.
Astrometry reduction is done using USNO-B1.0 catalog as reference.
From the residuals a general distortion pattern is derived. This vector field
of rersiduals produces a correction function which is then applied to the
measured coordinates to imporve the position accuracy. Comparison of
objects lying in overlapping frames indicates an internal accuracy of 0.03
Figure 5: Composite NIR intensity Galactic map observed by the DIRBE instrument on the Cosmic Background Explorer (COBE). Fields observed
mag for the photometric zero points and 0.2" for the astrometry.
with the TCS-CAIN survey are overplotted.