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

Title: H ii REGION G46.5-0.2: THE INTERPLAY BETWEEN IONIZING RADIATION, MOLECULAR GAS, AND STAR FORMATION

Abstract

H ii regions are particularly interesting because they can generate dense layers of gas and dust, elongated columns or pillars of gas pointing toward the ionizing sources, and cometary globules of dense gas where triggered star formation can occur. Understanding the interplay between the ionizing radiation and the dense surrounding gas is very important to explain the origin of these peculiar structures, and hence to characterize triggered star formation. G46.5-0.2 (G46), a poorly studied galactic H ii region located at about 4 kpc, is an excellent target for performing this kind of study. Using public molecular data extracted from the Galactic Ring Survey ({sup 13}CO J = 1–0) and from the James Clerk Maxwell Telescope data archive ({sup 12}CO, {sup 13}CO, C{sup 18}O J = 3–2, HCO{sup +}, and HCN J = 4–3), and infrared data from the GLIMPSE and MIPSGAL surveys, we perform a complete study of G46, its molecular environment, and the young stellar objects (YSOs) placed around it. We found that G46, probably excited by an O7V star, is located close to the edge of the GRSMC G046.34-00.21 molecular cloud. It presents a horse-shoe morphology opening in the direction of the cloud. We observed a filamentary structuremore » in the molecular gas likely related to G46 and not considerable molecular emission toward its open border. We found that about 10′ to the southwest of G46 there are some pillar-like features, shining at 8 μm and pointing toward the H ii region open border. We propose that the pillar-like features were carved and sculpted by the ionizing flux from G46. We found several YSOs likely embedded in the molecular cloud grouped in two main concentrations: one, closer to the G46 open border consisting of Class II type sources, and another mostly composed of Class I type YSOs located just ahead of the pillar-like features, strongly suggesting an age gradient in the YSO distribution.« less

Authors:
; ; ; ;  [1]; ; ; ; ;  [2];  [3]
  1. Instituto de Astronomía y Física del Espacio (IAFE, CONICET-UBA), CC 67, Suc. 28, 1428 Buenos Aires (Argentina)
  2. National Astronomical Observatories, Chinese Academy of Sciences, 20 A Datun Road, Chaoyang District, Beijing 100012 (China)
  3. Department of Astronomy, Peking University, 100871 Beijing (China)
Publication Date:
OSTI Identifier:
22520214
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 149; Journal Issue: 6; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON 13; CLOUDS; CONCENTRATION RATIO; COSMIC DUST; COSMIC GASES; HYDROCYANIC ACID; LAYERS; MOLECULES; MORPHOLOGY; STAR EVOLUTION; STARS; TELESCOPES

Citation Formats

Paron, S., Ortega, M. E., Dubner, G., Petriella, A., Giacani, E., Yuan, Jing-Hua, Li, Jin Zeng, Liu, Hongli, Huang, Ya Fang, Zhang, Si-Ju, and Wu, Yuefang, E-mail: sparon@iafe.uba.ar. H ii REGION G46.5-0.2: THE INTERPLAY BETWEEN IONIZING RADIATION, MOLECULAR GAS, AND STAR FORMATION. United States: N. p., 2015. Web. doi:10.1088/0004-6256/149/6/193.
Paron, S., Ortega, M. E., Dubner, G., Petriella, A., Giacani, E., Yuan, Jing-Hua, Li, Jin Zeng, Liu, Hongli, Huang, Ya Fang, Zhang, Si-Ju, & Wu, Yuefang, E-mail: sparon@iafe.uba.ar. H ii REGION G46.5-0.2: THE INTERPLAY BETWEEN IONIZING RADIATION, MOLECULAR GAS, AND STAR FORMATION. United States. doi:10.1088/0004-6256/149/6/193.
Paron, S., Ortega, M. E., Dubner, G., Petriella, A., Giacani, E., Yuan, Jing-Hua, Li, Jin Zeng, Liu, Hongli, Huang, Ya Fang, Zhang, Si-Ju, and Wu, Yuefang, E-mail: sparon@iafe.uba.ar. 2015. "H ii REGION G46.5-0.2: THE INTERPLAY BETWEEN IONIZING RADIATION, MOLECULAR GAS, AND STAR FORMATION". United States. doi:10.1088/0004-6256/149/6/193.
@article{osti_22520214,
title = {H ii REGION G46.5-0.2: THE INTERPLAY BETWEEN IONIZING RADIATION, MOLECULAR GAS, AND STAR FORMATION},
author = {Paron, S. and Ortega, M. E. and Dubner, G. and Petriella, A. and Giacani, E. and Yuan, Jing-Hua and Li, Jin Zeng and Liu, Hongli and Huang, Ya Fang and Zhang, Si-Ju and Wu, Yuefang, E-mail: sparon@iafe.uba.ar},
abstractNote = {H ii regions are particularly interesting because they can generate dense layers of gas and dust, elongated columns or pillars of gas pointing toward the ionizing sources, and cometary globules of dense gas where triggered star formation can occur. Understanding the interplay between the ionizing radiation and the dense surrounding gas is very important to explain the origin of these peculiar structures, and hence to characterize triggered star formation. G46.5-0.2 (G46), a poorly studied galactic H ii region located at about 4 kpc, is an excellent target for performing this kind of study. Using public molecular data extracted from the Galactic Ring Survey ({sup 13}CO J = 1–0) and from the James Clerk Maxwell Telescope data archive ({sup 12}CO, {sup 13}CO, C{sup 18}O J = 3–2, HCO{sup +}, and HCN J = 4–3), and infrared data from the GLIMPSE and MIPSGAL surveys, we perform a complete study of G46, its molecular environment, and the young stellar objects (YSOs) placed around it. We found that G46, probably excited by an O7V star, is located close to the edge of the GRSMC G046.34-00.21 molecular cloud. It presents a horse-shoe morphology opening in the direction of the cloud. We observed a filamentary structure in the molecular gas likely related to G46 and not considerable molecular emission toward its open border. We found that about 10′ to the southwest of G46 there are some pillar-like features, shining at 8 μm and pointing toward the H ii region open border. We propose that the pillar-like features were carved and sculpted by the ionizing flux from G46. We found several YSOs likely embedded in the molecular cloud grouped in two main concentrations: one, closer to the G46 open border consisting of Class II type sources, and another mostly composed of Class I type YSOs located just ahead of the pillar-like features, strongly suggesting an age gradient in the YSO distribution.},
doi = {10.1088/0004-6256/149/6/193},
journal = {Astronomical Journal (Online)},
number = 6,
volume = 149,
place = {United States},
year = 2015,
month = 6
}
  • AWe investigate the spatially resolved star formation relation using a galactic disk formed in a comprehensive high-resolution (3.8 pc) simulation. Our new implementation of stellar feedback includes ionizing radiation as well as supernova explosions, and we handle ionizing radiation by solving the radiative transfer equation rather than by a subgrid model. Photoheating by stellar radiation stabilizes gas against Jeans fragmentation, reducing the star formation rate (SFR). Because we have self-consistently calculated the location of ionized gas, we are able to make simulated, spatially resolved observations of star formation tracers, such as Hα emission. We can also observe how stellar feedbackmore » manifests itself in the correlation between ionized and molecular gas. Applying our techniques to the disk in a galactic halo of 2.3 × 10 11 M , we find that the correlation between SFR density (estimated from mock Hα emission) and H 2 density shows large scatter, especially at high resolutions of ≲ 75 pc that are comparable to the size of giant molecular clouds (GMCs). This is because an aperture of GMC size captures only particular stages of GMC evolution and because Hα traces hot gas around star-forming regions and is displaced from the H 2 peaks themselves. By examining the evolving environment around star clusters, we speculate that the breakdown of the traditional star formation laws of the Kennicutt-Schmidt type at small scales is further aided by a combination of stars drifting from their birthplaces and molecular clouds being dispersed via stellar feedback.« less
  • We investigate the spatially resolved star formation relation using a galactic disk formed in a comprehensive high-resolution (3.8 pc) simulation. Our new implementation of stellar feedback includes ionizing radiation as well as supernova explosions, and we handle ionizing radiation by solving the radiative transfer equation rather than by a subgrid model. Photoheating by stellar radiation stabilizes gas against Jeans fragmentation, reducing the star formation rate (SFR). Because we have self-consistently calculated the location of ionized gas, we are able to make simulated, spatially resolved observations of star formation tracers, such as Hα emission. We can also observe how stellar feedbackmore » manifests itself in the correlation between ionized and molecular gas. Applying our techniques to the disk in a galactic halo of 2.3 × 10{sup 11} M {sub ☉}, we find that the correlation between SFR density (estimated from mock Hα emission) and H{sub 2} density shows large scatter, especially at high resolutions of ≲75 pc that are comparable to the size of giant molecular clouds (GMCs). This is because an aperture of GMC size captures only particular stages of GMC evolution and because Hα traces hot gas around star-forming regions and is displaced from the H{sub 2} peaks themselves. By examining the evolving environment around star clusters, we speculate that the breakdown of the traditional star formation laws of the Kennicutt-Schmidt type at small scales is further aided by a combination of stars drifting from their birthplaces and molecular clouds being dispersed via stellar feedback.« less
  • Fabry-Perot spectrometry of H2 emission lines in the Cepheus A star-formation region is presented. It is found that the H2 emission in Cep A(E) is associated with dense condensations of NH3 and CS, while the emission in Cep A(W) is associated with Herbig-Haro objects and reflection nebulae. The data support the hypothesis that the two lobes of emission are produced by a single outflow originating from the region of maser and compact H II regions at the western edge of Cep A(E). 49 references.
  • The Multi-scale Continuum and Line Exploration of W49 is a comprehensive gas and dust survey of the giant molecular cloud (GMC) of W49A, the most luminous star-formation region in the Milky Way. The project covers, for the first time, the entire GMC at different scales and angular resolutions. In this paper, we present (1) an all-configuration Submillimeter Array mosaic in the 230 GHz (1.3 mm) band covering the central ∼3' × 3' (∼10 pc, known as W49N), where most of the embedded massive stars reside and (2) Purple Mountain Observatory 14 m telescope observations in the 90 GHz band, coveringmore » the entire GMC with maps of up to ∼35' × 35' in size, or ∼113 pc. We also make use of archival data from the Very Large Array, JCMT-SCUBA, the IRAM 30 m telescope, and the Caltech Submillimeter Observatory BOLOCAM Galactic Plane Survey. We derive the basic physical parameters of the GMC at all scales. Our main findings are as follows. (1) The W49 GMC is one of the most massive in the Galaxy, with a total mass M {sub gas} ∼ 1.1 × 10{sup 6} M {sub ☉} within a radius of 60 pc. Within a radius of 6 pc, the total gas mass is M {sub gas} ∼ 2 × 10{sup 5} M {sub ☉}. At these scales, only ∼1% of the material is photoionized. The mass reservoir is sufficient to form several young massive clusters (YMCs) as massive as a globular cluster. (2) The mass of the GMC is distributed in a hierarchical network of filaments. At scales <10 pc, a triple, centrally condensed structure peaks toward the ring of HC H II regions in W49N. This structure extends to scales from ∼10 to 100 pc through filaments that radially converge toward W49N and its less-prominent neighbor W49S. The W49A starburst most likely formed from global gravitational contraction with localized collapse in a 'hub-filament' geometry. (3) Currently, feedback from the central YMCs (with a present mass M {sub cl} ≳ 5 × 10{sup 4} M {sub ☉}) is still not enough to entirely disrupt the GMC, but further stellar mass growth could be enough to allow radiation pressure to clear the cloud and halt star formation. (4) The resulting stellar content will probably remain as a gravitationally bound massive star cluster or a small system of bound clusters.« less
  • We consider the relationship between molecular gas and star formation surface densities in 19 morphologically defined E/S0s with stellar mass {approx}<4 x 10{sup 10} M{sub sun}, paying particular attention to those found on the blue sequence in color versus stellar mass parameter space, where spiral galaxies typically reside. While some blue-sequence E/S0s must be young major-merger remnants, many low-mass blue-sequence E/S0s appear much less disturbed and may be experiencing the milder starbursts associated with inner-disk building as spirals (re)grow. For a sample of eight E/S0s (four blue, two mid, and two red sequence) whose CARMA CO(1-0), Spitzer MIPS 24 {mu}m,more » and GALEX FUV emission distributions are spatially resolved on a 750 pc scale, we find roughly linear relationships between molecular gas and star formation surface densities within all galaxies, with power-law indices N = 0.6-1.9 (median 1.2). Adding 11 more blue-sequence E/S0s whose CO(1-0) emission is not as well resolved, we find that most of our E/S0s have global 1-8 kpc aperture-averaged molecular gas surface densities overlapping the range spanned by the disks and centers of spiral galaxies. While many of our E/S0s fall on the same Schmidt-Kennicutt relation as local spirals, {approx}80% (predominantly on the blue sequence) are offset toward apparently higher molecular gas star formation efficiency (i.e., shorter molecular gas depletion time). Possible interpretations of the elevated efficiencies include bursty star formation similar to that in local dwarf galaxies, H{sub 2} depletion in advanced starbursts, or simply a failure of the CO(1-0) emission to trace all of the molecular gas.« less