skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: The Molecular Gas Environment in the 20 km s{sup −1} Cloud in the Central Molecular Zone

Abstract

We recently reported a population of protostellar candidates in the 20 km s{sup −1} cloud in the Central Molecular Zone of the Milky Way, traced by H{sub 2}O masers in gravitationally bound dense cores. In this paper, we report molecular line studies with high angular resolution (∼3″) of the environment of star formation in this cloud. Maps of various molecular line transitions as well as the continuum at 1.3 mm are obtained using the Submillimeter Array. Five NH{sub 3} inversion lines and the 1.3 cm continuum are observed with the Karl G. Jansky Very Large Array. The interferometric observations are complemented with single-dish data. We find that the CH{sub 3}OH, SO, and HNCO lines, which are usually shock tracers, are better correlated spatially with the compact dust emission from dense cores among the detected lines. These lines also show enhancement in intensities with respect to SiO intensities toward the compact dust emission, suggesting the presence of slow shocks or hot cores in these regions. We find gas temperatures of ≳100 K at 0.1 pc scales based on RADEX modeling of the H{sub 2}CO and NH{sub 3} lines. Although no strong correlations between temperatures and linewidths/H{sub 2}O maser luminosities are found,more » in high-angular-resolution maps we note several candidate shock-heated regions offset from any dense cores, as well as signatures of localized heating by protostars in several dense cores. Our findings suggest that at 0.1 pc scales in this cloud star formation and strong turbulence may together affect the chemistry and temperature of the molecular gas.« less

Authors:
;  [1]; ;  [2]; ;  [3];  [4];  [5]; ;  [6];  [7];  [8]
  1. School of Astronomy and Space Science, Nanjing University, Nanjing, Jiangsu 210093 (China)
  2. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  3. Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)
  4. Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom)
  5. Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, D-69120 Heidelberg (Germany)
  6. European Southern Observatory, Karl-Schwarzschild-Straße 2, D-85748 Garching (Germany)
  7. National Radio Astronomy Observatory, Socorro, NM 87801 (United States)
  8. Department of Physics and Astronomy, San Jose State University, One Washington Square, San Jose, CA 95192 (United States)
Publication Date:
OSTI Identifier:
22661174
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 839; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMMONIA; CLOUDS; CORRELATIONS; DUSTS; EMISSION; LINE WIDTHS; LUMINOSITY; MASERS; METHANOL; MILKY WAY; PROTOSTARS; RESOLUTION; SILICON OXIDES; SIMULATION; STARS; TURBULENCE; WATER

Citation Formats

Lu, Xing, Gu, Qiusheng, Zhang, Qizhou, Battersby, Cara, Kauffmann, Jens, Pillai, Thushara, Longmore, Steven N., Kruijssen, J. M. Diederik, Liu, Hauyu Baobab, Zhang, Zhi-Yu, Ginsburg, Adam, and Mills, Elisabeth A. C., E-mail: xinglv.nju@gmail.com. The Molecular Gas Environment in the 20 km s{sup −1} Cloud in the Central Molecular Zone. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA67F7.
Lu, Xing, Gu, Qiusheng, Zhang, Qizhou, Battersby, Cara, Kauffmann, Jens, Pillai, Thushara, Longmore, Steven N., Kruijssen, J. M. Diederik, Liu, Hauyu Baobab, Zhang, Zhi-Yu, Ginsburg, Adam, & Mills, Elisabeth A. C., E-mail: xinglv.nju@gmail.com. The Molecular Gas Environment in the 20 km s{sup −1} Cloud in the Central Molecular Zone. United States. doi:10.3847/1538-4357/AA67F7.
Lu, Xing, Gu, Qiusheng, Zhang, Qizhou, Battersby, Cara, Kauffmann, Jens, Pillai, Thushara, Longmore, Steven N., Kruijssen, J. M. Diederik, Liu, Hauyu Baobab, Zhang, Zhi-Yu, Ginsburg, Adam, and Mills, Elisabeth A. C., E-mail: xinglv.nju@gmail.com. Mon . "The Molecular Gas Environment in the 20 km s{sup −1} Cloud in the Central Molecular Zone". United States. doi:10.3847/1538-4357/AA67F7.
@article{osti_22661174,
title = {The Molecular Gas Environment in the 20 km s{sup −1} Cloud in the Central Molecular Zone},
author = {Lu, Xing and Gu, Qiusheng and Zhang, Qizhou and Battersby, Cara and Kauffmann, Jens and Pillai, Thushara and Longmore, Steven N. and Kruijssen, J. M. Diederik and Liu, Hauyu Baobab and Zhang, Zhi-Yu and Ginsburg, Adam and Mills, Elisabeth A. C., E-mail: xinglv.nju@gmail.com},
abstractNote = {We recently reported a population of protostellar candidates in the 20 km s{sup −1} cloud in the Central Molecular Zone of the Milky Way, traced by H{sub 2}O masers in gravitationally bound dense cores. In this paper, we report molecular line studies with high angular resolution (∼3″) of the environment of star formation in this cloud. Maps of various molecular line transitions as well as the continuum at 1.3 mm are obtained using the Submillimeter Array. Five NH{sub 3} inversion lines and the 1.3 cm continuum are observed with the Karl G. Jansky Very Large Array. The interferometric observations are complemented with single-dish data. We find that the CH{sub 3}OH, SO, and HNCO lines, which are usually shock tracers, are better correlated spatially with the compact dust emission from dense cores among the detected lines. These lines also show enhancement in intensities with respect to SiO intensities toward the compact dust emission, suggesting the presence of slow shocks or hot cores in these regions. We find gas temperatures of ≳100 K at 0.1 pc scales based on RADEX modeling of the H{sub 2}CO and NH{sub 3} lines. Although no strong correlations between temperatures and linewidths/H{sub 2}O maser luminosities are found, in high-angular-resolution maps we note several candidate shock-heated regions offset from any dense cores, as well as signatures of localized heating by protostars in several dense cores. Our findings suggest that at 0.1 pc scales in this cloud star formation and strong turbulence may together affect the chemistry and temperature of the molecular gas.},
doi = {10.3847/1538-4357/AA67F7},
journal = {Astrophysical Journal},
number = 1,
volume = 839,
place = {United States},
year = {Mon Apr 10 00:00:00 EDT 2017},
month = {Mon Apr 10 00:00:00 EDT 2017}
}
  • We report the discovery of a population of deeply embedded protostellar candidates in the 20 km s{sup −1} cloud, one of the massive molecular clouds in the Central Molecular Zone (CMZ) of the Milky Way, using interferometric submillimeter continuum and H{sub 2}O maser observations. The submillimeter continuum emission shows five 1 pc scale clumps, each of which further fragments into several 0.1 pc scale cores. We identify 17 dense cores, among which 12 are gravitationally bound. Among the 18 H{sub 2}O masers detected, 13 coincide with the cores and probably trace outflows emanating from the protostars. There are also 5more » gravitationally bound dense cores without H{sub 2}O maser detection. In total, the 13 masers and 5 cores may represent 18 protostars with spectral types later than B1 or potentially growing more massive stars at earlier evolutionary stages, given the non-detection in the centimeter radio continuum. In combination with previous studies of CH{sub 3}OH masers, we conclude that the star formation in this cloud is at an early evolutionary phase, before the presence of any significant ionizing or heating sources. Our findings indicate that star formation in this cloud may be triggered by a tidal compression as it approaches pericenter, similar to the case of G0.253+0.016 but with a higher star formation rate, and demonstrate that high angular resolution, high-sensitivity maser, and submillimeter observations are promising techniques to unveil deeply embedded star formation in the CMZ.« less
  • This paper reports the discovery of evidence for physical contact between the Galactic circumnuclear disk (CND) and an exterior giant molecular cloud. The central 10 pc of our Galaxy has been imaged in the HCN J  = 1–0, HCO{sup +} J  = 1–0, CS J  = 2–1, H{sup 13}CN J  = 1–0, SiO J  = 2–1, SO N{sub J}  = 2{sub 3}–1{sub 2}, and HC{sub 3}N J  = 11–10 lines using the Nobeyama Radio Observatory 45 m radio telescope. Based on our examination of the position–velocity maps of several high-density probe lines, we have found that an emission “bridge” may be connecting the +20 km s{sup −1} cloudmore » (M–0.13–0.08) and the negative-longitude extension of the CND. Analyses of line intensity ratios imply that the chemical property of the bridge is located between the +20 km s{sup −1} cloud and the CND. We introduce a new interpretation that a part of the CND may be colliding with the 20 km s{sup −1} cloud and the collision may be responsible for the formation of the bridge. Such collisional events could promote mass accretion onto the CND or into the inner ionized cavity, which may be further tested by proper motion studies.« less
  • The feedback from galactic outflows is thought to play an important role in shaping the gas content, star formation history, and ultimately the stellar mass function of galaxies. Here we present evidence for massive molecular outflows associated with ultra-luminous infrared galaxies (ULIRGs) in the co-added Redshift Search Receiver {sup 12}CO (1-0) spectrum. Our stacked spectrum of 27 ULIRGs at z = 0.043-0.11 ({nu}{sub rest} = 110-120 GHz) shows broad wings around the CO line with {Delta}V(FWZI) {approx} 2000 km s{sup -1}. Its integrated line flux accounts for up to 25% {+-} 5% of the total CO line luminosity. When interpretedmore » as a massive molecular outflow wind, the associated mechanical energy can be explained by a concentrated starburst with star formation rate (SFR) {>=}100 M{sub sun} yr{sup -1}, which agrees well with their SFR derived from the FIR luminosity. Using the high signal-to-noise stacked composite spectrum, we also probe {sup 13}CO and {sup 12}CN emission in the sample and discuss how the chemical abundance of molecular gas may vary depending on the physical conditions of the nuclear region.« less
  • We report 350 and 230 GHz observations of molecular gas and dust in the starburst nucleus of NGC 253 at 20-40 pc (1''-2'') resolution. The data contain CO(3-2), HCN(4-3), CO(2-1), {sup 13}CO(2-1), C{sup 18}O(2-1), and continuum at 0.87 mm and 1.3 mm toward the central kiloparsec. The CO(2-1) size of the galaxy's central molecular zone (CMZ) is measured to be about 300 pcx100 pc at the half-maximum of intensity. Five clumps of dense and warm gas stand out in the CMZ at arcsecond resolution, and they are associated with compact radio sources due to recent massive star formation. They contributemore » one-third of the CO emission in the central 300 pc and have {sup 12}CO peak brightness temperatures around 50 K, molecular gas column densities on the order of 10{sup 4} M{sub sun} pc{sup -2}, gas masses on the order of 10{sup 7} M{sub sun} in the size scale of 20 pc, volume-averaged gas densities of n{sub H{sub 2}} {approx} 4000 cm{sup -3}, and high HCN-to-CO ratios suggestive of higher fractions of dense gas than in the surrounding environment. It is suggested that these are natal molecular cloud complexes of massive star formation. The CMZ of NGC 253 is also compared with that of our Galaxy in CO(2-1) at the same 20 pc resolution. Their overall gas distributions are strikingly similar. The five molecular cloud complexes appear to be akin to such molecular complexes as Sgr A, Sgr B2, Sgr C, and the l = 1.{sup 0}3 cloud in the Galactic center. On the other hand, the starburst CMZ in NGC 253 has higher temperatures and higher surface (and presumably volume) densities than its non-starburst cousin.« less
  • Although recent determinations of the distance to the Virgo cluster based on Cepheid variable stars represent an important step in pinning down the Hubble constant, after 65 years a definitive determination of the Hubble constant still eludes cosmologists. At present, most of the observational determinations place the Hubble constant between 40 and 90 kilometers per second per megaparsec (km s{sup -1} Mpc{sup -1}). The case is made here for a Hubble constant that is even smaller than the lower bound of the accepted range on the basis of the great advantages, all theoretical in nature, of a Hubble constant ofmore » around 30 kilometers per second per megaparsec. Such a value for the Hubble cures all of the wills of the current theoretical orthodoxy, that is, a spatially flat universe composed predominantly of cold dark matter. 42 refs., 4 figs.« less