J/ApJ/853/171 mm point sources in the extended Sgr B2 cloud (Ginsburg+, 2018)
Distributed star formation throughout the galactic center cloud Sgr B2.
Ginsburg A., Bally J., Barnes A., Bastian N., Battersby C., Beuther H.,
Brogan C., Contreras Y., Corby J., Darling J., De Pree C., Galvan-Madrid R.,
Garay G., Henshaw J., Hunter T., Kruijssen J.M.D., Longmore S., Lu X.,
Meng F., Mills E.A.C., Ott J., Pineda J.E., Sanchez-Monge A., Schilke P.,
Schmiedeke A., Walker D., Wilner D.
<Astrophys. J., 853, 171 (2018)>
=2018ApJ...853..171G 2018ApJ...853..171G
ADC_Keywords: Molecular clouds; H II regions; YSOs; Millimetric/submm sources
Keywords: galaxies: star formation; H II regions; ISM: molecules;
stars: formation; stars: protostars
Abstract:
We report ALMA observations with resolution ∼0.5" at 3mm of the
extended Sgr B2 cloud in the Central Molecular Zone (CMZ). We detect
271 compact sources, most of which are smaller than 5000au. By ruling
out alternative possibilities, we conclude that these sources consist
of a mix of hypercompact HII regions and young stellar objects (YSOs).
Most of the newly detected sources are YSOs with gas envelopes that,
based on their luminosities, must contain objects with stellar masses
M*≳8M☉. Their spatial distribution spread over a ∼12x3pc region
demonstrates that Sgr B2 is experiencing an extended star formation
event, not just an isolated "starburst" within the protocluster
regions. Using this new sample, we examine star formation thresholds
and surface density relations in Sgr B2. While all of the YSOs reside
in regions of high column density (N(H2)≳2x1023cm-2), not all
regions of high column density contain YSOs. The observed column
density threshold for star formation is substantially higher than that
in solar vicinity clouds, implying either that high-mass star
formation requires a higher column density or that any star formation
threshold in the CMZ must be higher than in nearby clouds. The
relation between the surface density of gas and stars is incompatible
with extrapolations from local clouds, and instead stellar densities
in Sgr B2 follow a linear Σ*-Σgas relation, shallower
than that observed in local clouds. Together, these points suggest
that a higher volume density threshold is required to explain star
formation in CMZ clouds.
Description:
Data were acquired as part of ALMA project 2013.1.00269.S.
Observations were taken in ALMA Band 3 with the 12m Total Power array
(spanning 2015 Jan 25 to 2015 May 18), with the ALMA ACA 7m array on
2014 Jul 01, 02 and 03, and in two configurations with the ALMA 12m
array (between 2014 Dec 06 and 2015 Jul 02). The basebands were
centered at 89.48, 91.28, 101.37, and 103.23GHz with bandwidth
1.875GHz (total 7.5GHz).
We use Herschel 70-350um (Molinari+ 2010A&A...518L.100M 2010A&A...518L.100M), the James
Clerk Maxwell Telescope (JCMT) SCUBA 450um (Pierce-Price+
2000ApJ...545L.121P 2000ApJ...545L.121P and Di Francesco+ 2008, J/ApJS/175/277) and the
10.4m Caltech Submillimeter Observatory (CSO) SHARC 350um (Bally+,
J/ApJ/721/137) archival data to create column density maps at a
coarser resolution than the ALMA data. See section 2.2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 134 297 Continuum source identifiers and photometry
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See also:
VIII/96 : 6-GHz methanol multibeam maser catalogue (Caswell+, 2010-12)
J/A+A/291/943 : Protostellar cores (Ossenkopf+, 1994)
J/ApJS/155/577 : H2O masers in W49 North and Sagittarius B2 (McGrath+, 2004)
J/ApJS/155/421 : Survey of Galactic Center region at 20cm (Yusef-Zadeh+, 2004)
J/ApJS/175/277 : Submillimeter-Continuum SCUBA detections (Di Francesco+, 2008)
J/A+A/487/993 : MAMBO Mapping of c2d Clouds and Cores (Kauffmann+, 2008)
J/ApJS/181/321 : Properties of Spitzer c2d dark clouds (Evans+, 2009)
J/ApJS/184/18 : Spitzer survey of young stellar clusters (Gutermuth+, 2009)
J/ApJS/181/110 : Galactic center X-ray sources (Muno+, 2009)
J/ApJ/702/178 : YSOs in the central 400pc of the Galaxy (Yusef-Zadeh+, 2009)
J/ApJ/721/137 : The Bolocam Galactic Plane Survey (BGPS) (Bally+, 2010)
J/ApJ/723/1019 : Galactic SFR and gas surface densities (Heiderman+, 2010)
J/ApJS/208/9 : Intrinsic colors and temperatures of PMS stars (Pecaut+, 2013)
J/A+A/568/A56 : mm continuum and line images of G0.253+0.016 (Johnston+, 2014)
J/A+A/566/A45 : Orion optical-depth and column-density maps (Lombardi+, 2014)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/ApJS/213/1 : The MSFRs Omnibus X-ray Catalog (MOXC) (Townsley+, 2014)
J/ApJ/830/17 : GC secondary IR astrometric standards (Boehle+, 2016)
J/ApJS/224/5 : Herschel Orion Protostar Survey (HOPS) SEDs (Furlan+, 2016)
J/A+A/586/A50 : Central Molecular Zone H2CO temperature maps (Ginsburg+, 2016)
J/A+A/595/A94 : Temp. structures in Galactic center clouds (Immer+, 2016)
J/A+A/591/A149 : Hi-GAL. inner Milky Way: +68≥l≥70 (Molinari+, 2016)
J/A+A/588/A30 : Properties of cores in OMC 2/3 (Sadavoy+, 2016)
J/A+A/606/A100 : YSOs in California Molecular Cloud (Lada+, 2017)
J/A+A/604/A6 : SgrB2 ALMA continuum and spectral index (Sanchez-Monge+, 2017)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- ID Identifier (1)
8- 14 A7 --- OID Other identifier
16- 28 F13.9 deg RAdeg [266.78/266.88] Right Ascension (J2000)
30- 43 F14.10 deg DEdeg [-28.5/-28.3] Declination (J2000)
45- 46 A2 --- Clust Cluster code (2)
48 A1 --- n_ID S=strong source; W=weak or low-confidence
source
49 A1 --- M09 X=match with Muno+ 2009, J/ApJS/181/110
Chandra X-ray source catalog ("_"=no match)
50 A1 --- C10 M=match with Caswell+ 2010, VIII/96
Methanol Multibeam Survey CH3OH maser cat.
51 A1 --- M04 W=match with McGrath+ 2004, J/ApJS/155/577
water maser survey ("_"=no match)
53- 63 A11 --- Class Simbad object type
65- 72 F8.3 mJy/beam Smax [0/1640] Peak flux density
74- 80 F7.3 K TBmax [0/861] Brightness temperature
82- 90 F9.4 mJy Stot [0.01/2390]? Integrated flux density;
within a 0.5" radius beam
92- 98 F7.4 mJy/beam sigmabg [0/49] Background RMS flux level
100-107 F8.5 --- alpha [-7/11] Spectral index
109-117 F9.6 --- e_alpha [0/12.6] Error in alpha
119-125 F7.2 Msun M40K [0/1160]? Mass (3)
127-134 E8.2 cm-2 NH2 [0/3.6e+26]? H2 column density (3)
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Note (1): "FNa" identifiers are <[BJ84] FNa> in Simbad;
"ANN.NN" are <[GCD95] NN.NN> in Simbad; and
"A" identifiers are in Simbad.
Note (2): The clusters are M, N, S and NE. Sources with no cluster association
are marked with "--".
Note (3): Assuming a dust temperature of 40K. The first 18 entries have blank
values because their observed intensity is inconsistent with an
assumed dust temperature of 40K.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-Oct-2018