J/ApJS/205/5 YSO candidates in nearby molecular clouds (Hsieh+, 2013)
Populations of young stellar objects in nearby molecular clouds.
Hsieh T.-H., Lai S.-P.
<Astrophys. J. Suppl. Ser., 205, 5 (2013)>
=2013ApJS..205....5H 2013ApJS..205....5H
ADC_Keywords: YSOs ; Stars, pre-main sequence ; Molecular clouds
Keywords: brown dwarfs - ISM: clouds - stars: formation - stars: protostars -
stars: luminosity function, mass function - stars: pre-main sequence
Abstract:
We develop a new method for identifying young stellar objects (YSOs)
from star-forming regions using the photometry data from Spitzer's c2d
Legacy Project. The aim is to obtain YSO lists as complete as possible
for studying statistical properties such as the star formation rate
(SFR) and lifetimes of YSOs in different evolutionary stages. The
largest obstacle in identifying YSOs comes from background galaxies
with similar spectral energy distributions to YSOs. Traditionally,
selected color-color and color-magnitude criteria are used to separate
YSOs and galaxies. However, since there is no obvious boundary between
YSOs and galaxies in color-color diagrams and color-magnitude diagrams
(CMDs), those criteria may exclude faint YSOs near the boundary. In
this paper, we separate the YSOs and galaxies in a multi-dimensional
(multi-D) magnitude space, which is equivalent to using all variations
of CMDs simultaneously. Comparing sources from molecular clouds to
Spitzer's SWIRE data, which have a negligible amount of YSOs, we can
naturally identify YSO candidates (YSOc) located outside of the
galaxy-populated regions in the multi-D space. In the five c2d
surveyed clouds, we select 322 new YSOc and miss/exclude 33 YSOc
compared to Evans et al. (2009, Cat. J/ApJS/181/321), and this results
in 1313 YSOc in total. As a result, SFR increases 28% correspondingly,
but the lifetimes of YSOs in different evolutionary stages remain
unchanged. Compared to theories by Krumholz & McKee
(2005ApJ...630..250K 2005ApJ...630..250K), our derived SFR suggests that star formation at
a large scale is dominated by supersonic turbulence rather than
magnetic fields. Furthermore, we identify seven new very low
luminosity objects.
Description:
The data we used in this paper are from two Spitzer Legacy Projects,
c2d (Evans et al. 2007, Final Delivery of Data from the c2d Legacy
Project: IRAC and MIPS (Pasadena, CA: SSC)) and SWIRE (same data as in
Harvey et al., 2007, Cat. J/ApJ/663/1149).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 114 1313 YSO candidates in 5 nearby molecular clouds
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See also:
II/290 : SWIRE Photometric Redshift Catalogue (Rowan-Robinson+, 2008)
J/MNRAS/410/2662 : AMI 1.8cm observations in c2d small clouds (Scaife+, 2011)
J/MNRAS/415/893 : AMI-LA 16 GHz sources in Perseus region (Scaife+, 2011)
J/ApJ/724/835 : The Spitzer c2d survey of WTTSs. III. (Wahhaj+, 2010)
J/ApJS/181/321 : Properties of Spitzer c2d dark clouds (Evans+, 2009)
J/ApJS/177/551 : Spitzer c2d survey of Lupus dark clouds (Merin+, 2008)
J/A+A/487/993 : MAMBO Mapping of c2d Clouds and Cores (Kauffmann+, 2008)
J/ApJ/676/427 : MIPS and IRAC data on ChaII PMS stars (Alcala+, 2008)
J/AJ/133/1560 : Spitzer c2d small clouds and cores (Wu+, 2007)
J/ApJ/663/1149 : Spitzer survey of Serpens YSO population (Harvey+, 2007)
J/ApJ/667/308 : Weak-line T Tauri in Spitzer c2d Survey. II. (Cieza+, 2007)
J/ApJ/638/293 : 1.1mm sources in the Perseus Molecular Cloud (Enoch+, 2006)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Cloud Cloud identifier (Chamaeleon II, Lupus,
Ophiuchus, Perseus or Serpens)
15- 25 F11.7 deg RAdeg Right Ascension in decimal degrees (J2000)
27- 37 F11.7 deg DEdeg Declination in decimal degrees (J2000)
39- 43 F5.2 [-] galP1 [-4.16/1.4]? log of galaxy probability 1 (1)
45- 48 A4 --- f_galP1 [-inf, sat, cde] Flag on galP1 (4)
50- 54 F5.2 [-] galP2 [-3.33/2.45]? log of galaxy probability 2 (1)
56- 59 A4 --- f_galP2 [-inf] -inf = -infinity (probability=0)
61- 65 F5.2 [-] galP1p [-4.16/1.54]? log of galaxy probability 1p (1)
67- 70 A4 --- f_galP1p [-inf] -inf = -infinity (probability=0)
72- 76 F5.2 [-] galP2p [-3.76/2.85]? log of galaxy probability 2p (1)
78- 81 A4 --- f_galP2p [-inf] -inf = -infinity (probability=0)
83- 87 F5.2 [pc-2] Den [-0.95/3.65]? log of stellar density
89- 92 F4.2 [-] YSOP [0/2.31]? YSO probability (1)
94-112 A19 --- Class c2d classification (2)
114 A1 --- f_Class [ab] Flag on Class (3)
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Note (1): the "probabilities" (galaxy probability or YSO probability) are
not a probability for a source to be a galaxy (or an YSO), but an
unnormalized number which indicates how many galaxies (or YSOs) are
near a specific position in the multi-dimensional photometric space.
We calculate four galaxy probabilities (1, 2, 1p and 2p), where
probability 1 is computed from (J, Ks, IR2, IR4, MP1) and probability
2 from (IR1, IR2, IR3, IR4, MP1) arrays or their subarrays (see
section 3.2 for details); the probabilities 1p and 2p are the galaxy
density from the arrays discounting the bands with image type (PSF
fitting) differing from 1 (high uncertainty in photometry resulting
from a low signal-to-noise ratio, extended size, or non-circular
shape, etc; see section 2.1)
Note (2): If the c2d source type does not contain "YSO", the source is
added to the YSO candidates (YSOc) list by Evans literature. Sources
without c2d classification are left blank and are newly identified
YSOc from this work.
Note (3): Flag as follows:
a = This source is IRAS 03292+3039. The c2d automated pipeline divide
this source into two sources. We use the flux provided by Jorgensen
et al. (2006ApJ...645.1246J 2006ApJ...645.1246J) which treats it as a single source.
b = Only J-IR4 bands are used, since MP1 flux is band-filled and may
contain contribution from a nearby YSO candidate 4arcsec away
(246.8152985-24.6458768).
Note (4): Flag mean the following:
-inf = -infinity (probability is zero)
sat = saturate
c = source DK Cha
d = source IRAS16293-2422B
e = source VLA1623
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 18-Mar-2013