scholarly journals Raman mapping of photodissociation regions

2021 ◽  
Author(s):  
William J Henney
Keyword(s):  
Raman Scattering ◽  
Neutral Hydrogen ◽  
High Mass ◽  
Ionization Front ◽  
Orion Nebula ◽  
Star Forming ◽  
Spatially Resolved ◽  
Neutral Gas ◽  
Far Ultraviolet ◽  
Hydrogen Lines

Abstract Broad Raman-scattered wings of hydrogen lines can be used to map neutral gas illuminated by high-mass stars in star forming regions. Raman scattering transforms far-ultraviolet starlight from the wings of the Lyβ line (1022Å to 1029Å) to red visual light in the wings of the Hα line (6400AA to 6700Å). Analysis of spatially resolved spectra of the Orion Bar and other regions in the Orion Nebula shows that this process occurs in the neutral photo-dissociation region between the ionization front and dissociation front. The inner Raman wings are optically thick and allow the neutral hydrogen density to be determined, implying n(H0) ≈ 105 cm−3 for the Orion Bar. Far-ultraviolet resonance lines of neutral oxygen imprint their absorption onto the stellar continuum as it passes through the ionization front, producing characteristic absorption lines at 6633Å and 6664Å with widths of order 2Å. This is a unique signature of Raman scattering, which allows it to be easily distinguished from other processes that might produce broad Hα wings, such as electron scattering or high-velocity outflows.

scholarly journals Do star clusters form in a completely mass-segregated way?

2019 ◽  
Vol 626 ◽  
pp. A79 ◽  
Author(s):  
Václav Pavlík ◽  
Pavel Kroupa ◽  
Ladislav Šubr
Keyword(s):  
Star Clusters ◽  
Point Of View ◽  
High Mass ◽  
Orion Nebula ◽  
Energy Redistribution ◽  
X Ray ◽  
Star Forming ◽  
Independent Observations ◽  
Mass Segregation ◽  
Rule Out

Context. ALMA observations of the Serpens South star-forming region suggest that stellar protoclusters may be completely mass segregated at birth. Independent observations also suggest that embedded clusters form segregated by mass. Aims. As the primordial mass segregation seems to be lost over time, we aim to study on which timescale an initially perfectly mass-segregated star cluster becomes indistinguishable from an initially not mass-segregated cluster. As an example, the Orion Nebula Cluster (ONC) is also discussed. Methods. We used N-body simulations of star clusters with various masses and two different degrees of primordial mass segregation. We analysed their energy redistribution through two-body relaxation to quantify the time when the models agree in terms of mass segregation, which sets in only dynamically in the models that are primordially not mass segregated. A comprehensive cross-matched catalogue combining optical, infrared, and X-ray surveys of ONC members was also compiled and made available. Results. The models evolve to a similar radial distribution of high-mass stars after the core collapse (about half a median two-body relaxation time, trh) and become observationally indistinguishable from the point of view of mass segregation at time τv ≈ 3.3 trh. In the case of the ONC, using the distribution of high-mass stars, we may not rule out either evolutionary scenario (regardless of whether they are initially mass segregated). When we account for extinction and elongation of the ONC, as reported elsewhere, an initially perfectly mass-segregated state seems to be more consistent with the observed cluster.

scholarly journals Chemical differentiation in Sagittarius B2(N): first high resolution results

2013 ◽  
Vol 9 (S303) ◽  
pp. 205-207
Author(s):  
J. F. Corby ◽  
P. A. Jones ◽  
M. R. Cunningham ◽  
A. J. Remijan
Keyword(s):  
Organic Chemistry ◽  
High Resolution ◽  
Galactic Center ◽  
High Mass ◽  
Mass Star ◽  
Radio Interferometry ◽  
Broad Bandwidth ◽  
Star Forming ◽  
Spatially Resolved ◽  
Line Survey

AbstractSgr B2 is an active high mass star forming region in the Galactic center and the pre-eminent interstellar source of organic chemistry. Newly available broad bandwidth radio interferometry data enables a spatially resolved study of the chemical environments within the Sgr B2(N) core. We present selections from a 30 - 50 GHz spectral line survey conducted with the ATCA.

scholarly journals Outflows in star-forming galaxies: Stacking analyses of resolved winds and the relation to their hosts’ properties

2020 ◽  
Vol 493 (3) ◽  
pp. 3081-3097 ◽  
Author(s):  
G W Roberts-Borsani ◽  
A Saintonge ◽  
K L Masters ◽  
D V Stark
Keyword(s):  
High Mass ◽  
Critical Threshold ◽  
Star Forming ◽  
Neutral Gas ◽  
The Galaxy ◽  
Central Regions ◽  
Mass Outflow ◽  
Main Regulator ◽  
Star Formation Histories ◽  
Gas Cycling

ABSTRACT Outflows form an integral component in regulating the gas cycling in and out of galaxies, although their impact on the galaxy hosts is still poorly understood. Here we present an analysis of 405 high mass (log M*/M⊙ ≥ 10), star-forming galaxies (excluding AGN) with low inclinations at z ∼ 0, using stacking techniques of the Na D λλ5889, 5895 Å neutral gas tracer in IFU observations from the MaNGA DR15 survey. We detect outflows in the central regions of 78/405 galaxies and determine their extent and power through the construction of stacked annuli. We find outflows are most powerful in central regions and extend out to ∼1Re, with declining mass outflow rates and loading factors as a function of radius. The stacking of spaxels over key galaxy quantities reveals outflow detections in regions of high ΣSFR (≳0.01 M⊙ yr−1 kpc−2) and $\Sigma _{M_{*}}$ (≳107 M⊙ kpc−2) along the resolved main sequence. Clear correlations with ΣSFR suggest it is the main regulator of outflows, with a critical threshold of ∼0.01 M⊙ yr−1 kpc−2 needed to escape the weight of the disc and launch them. Furthermore, measurements of the Hδ and Dn4000 indices reveal virtually identical star formation histories between galaxies with outflows and those without. Finally, through stacking of H i 21 cm observations for a subset of our sample, we find outflow galaxies show reduced H i gas fractions at central velocities compared to their non-detection control counterparts, suggestive of some removal of H i gas, likely in the central regions of the galaxies, but not enough to completely quench the host.

scholarly journals The anatomy of a star-forming galaxy II: FUV heating via dust

2020 ◽  
Vol 499 (2) ◽  
pp. 2028-2041
Author(s):  
S M Benincasa ◽  
J W Wadsley ◽  
H M P Couchman ◽  
A R Pettitt ◽  
B W Keller ◽  
...  
Keyword(s):  
Star Formation ◽  
Energy Budget ◽  
Star Clusters ◽  
Young Star ◽  
Star Forming ◽  
Neutral Gas ◽  
Feedback Model ◽  
Science Application ◽  
Far Ultraviolet ◽  
Young Star Clusters

ABSTRACT Far-ultraviolet (FUV) radiation greatly exceeds UV, supernovae (SNe), and winds in the energy budget of young star clusters but is poorly modelled in galaxy simulations. We present results of the first isolated galaxy disc simulations to include photoelectric heating of gas via dust grains from FUV radiation self-consistently, using a ray-tracing approach that calculates optical depths along the source–receiver sightline. This is the first science application of the TREVR radiative transfer algorithm. We find that FUV radiation alone cannot regulate star formation. However, FUV radiation produces warm neutral gas and is able to produce regulated galaxies with realistic scale heights. FUV is also a long-range feedback and is more important in the outer discs of galaxies. We also use the superbubble feedback model, which depends only on the SN energy per stellar mass, is more physically realistic than common, parameter-driven alternatives and thus better constrains SN feedback impacts. FUV and SNe together can regulate star formation without producing too much hot ionized medium and with less disruption to the interstellar medium compared to SNe alone.

scholarly journals How do central and satellite galaxies quench? – Insights from spatially resolved spectroscopy in the MaNGA survey

2020 ◽  
Vol 499 (1) ◽  
pp. 230-268 ◽  
Author(s):  
Asa F L Bluck ◽  
Roberto Maiolino ◽  
Joanna M Piotrowska ◽  
James Trussler ◽  
Sara L Ellison ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Environmental Parameters ◽  
Single Parameter ◽  
High Mass ◽  
Star Forming ◽  
Spatially Resolved ◽  
Radial Profiles ◽  
Satellite Galaxies ◽  
Spatially Resolved Spectroscopy

ABSTRACT We investigate how star formation quenching proceeds within central and satellite galaxies using spatially resolved spectroscopy from the SDSS-IV MaNGA DR15. We adopt a complete sample of star formation rate surface densities (ΣSFR), derived in Bluck et al. (2020), to compute the distance at which each spaxel resides from the resolved star forming main sequence (ΣSFR − Σ* relation): ΔΣSFR. We study galaxy radial profiles in ΔΣSFR, and luminosity weighted stellar age (AgeL), split by a variety of intrinsic and environmental parameters. Via several statistical analyses, we establish that the quenching of central galaxies is governed by intrinsic parameters, with central velocity dispersion (σc) being the most important single parameter. High mass satellites quench in a very similar manner to centrals. Conversely, low mass satellite quenching is governed primarily by environmental parameters, with local galaxy overdensity (δ5) being the most important single parameter. Utilizing the empirical MBH − σc relation, we estimate that quenching via AGN feedback must occur at $M_{\rm BH} \ge 10^{6.5-7.5} \, \mathrm{M}_{\odot }$, and is marked by steeply rising ΔΣSFR radial profiles in the green valley, indicating ‘inside-out’ quenching. On the other hand, environmental quenching occurs at overdensities of 10–30 times the average galaxy density at z∼ 0.1, and is marked by steeply declining ΔΣSFR profiles, indicating ‘outside-in’ quenching. Finally, through an analysis of stellar metallicities, we conclude that both intrinsic and environmental quenching must incorporate significant starvation of gas supply.

scholarly journals Small Protoplanetary Disks in the Orion Nebula Cluster and OMC1 with ALMA

2021 ◽  
Vol 923 (2) ◽  
pp. 221
Author(s):  
Justin Otter ◽  
Adam Ginsburg ◽  
Nicholas P. Ballering ◽  
John Bally ◽  
J. A. Eisner ◽  
...  
Keyword(s):  
Orion Nebula ◽  
Nearby Star ◽  
Star Forming ◽  
Spatially Resolved ◽  
Star Forming Regions ◽  
Two Samples ◽  
Disk Evolution ◽  
The Impact ◽  
Strong Radiation ◽  
Stellar Density

Abstract The Orion Nebula Cluster (ONC) is the nearest dense star-forming region at ∼400 pc away, making it an ideal target to study the impact of high stellar density and proximity to massive stars (the Trapezium) on protoplanetary disk evolution. The OMC1 molecular cloud is a region of high extinction situated behind the Trapezium in which actively forming stars are shielded from the Trapezium’s strong radiation. In this work, we survey disks at high resolution with Atacama Large Millimeter/submillimeter Array at three wavelengths with resolutions of 0.″095 (3 mm; Band 3), 0.″048 (1.3 mm; Band 6), and 0.″030 (0.85 mm; Band 7) centered on radio Source I. We detect 127 sources, including 15 new sources that have not previously been detected at any wavelength. 72 sources are spatially resolved at 3 mm, with sizes from ∼8–100 au. We classify 76 infrared-detected sources as foreground ONC disks and the remainder as embedded OMC1 disks. The two samples have similar disk sizes, but the OMC1 sources have a dense and centrally concentrated spatial distribution, indicating they may constitute a spatially distinct subcluster. We find smaller disk sizes and a lack of large (>75 au) disks in both our samples compared to other nearby star-forming regions, indicating that environmental disk truncation processes are significant. While photoevaporation from nearby massive Trapezium stars may account for the smaller disks in the ONC, the embedded sources in OMC1 are hidden from this radiation and thus must truncated by some other mechanism, possibly dynamical truncation or accretion-driven contraction.

scholarly journals Redshift evolution of the H2/H i mass ratio in galaxies

2021 ◽  
Vol 502 (1) ◽  
pp. L85-L89
Author(s):  
Laura Morselli ◽  
A Renzini ◽  
A Enia ◽  
G Rodighiero
Keyword(s):  
High Redshift ◽  
Strong Dependence ◽  
Formation Rate ◽  
Stellar Mass ◽  
Mass Ratio ◽  
Star Forming ◽  
Spatially Resolved ◽  
Internal Working ◽  
Neutral Gas ◽  
Grand Design

ABSTRACT In this paper, we present an attempt to estimate the redshift evolution of the molecular to neutral gas mass ratio within galaxies (at fixed stellar mass). For a sample of five nearby grand design spirals located on the main-sequence (MS) of star-forming galaxies, we exploit maps at 500 pc resolution of stellar mass and star formation rate (M⋆ and SFR). For the same cells, we also have estimates of the neutral (MH i) and molecular ($M_{\rm H_2}$) gas masses. To compute the redshift evolution, we exploit two relations: (i) one between the molecular-to-neutral mass ratio and the total gas mass (Mgas), whose scatter shows a strong dependence with the distance from the spatially resolved MS, and (ii) the one between $\log (M_{\rm {H_2}}/M_{\star })$ and log (MH i/M⋆). For both methods, we and that $M_{\rm H_2}$/MH i within the optical radius slightly decreases with redshift, contrary to common expectations of galaxies becoming progressively more dominated by molecular hydrogen at high redshifts. We discuss possible implications of this trend on our understanding of the internal working of high-redshift galaxies.

scholarly journals Evolution of the cold gas fraction and the star formation history: Prospects with current and future radio facilities

2018 ◽  
Vol 35 ◽  
Author(s):  
S. J. Curran
Keyword(s):  
Star Formation ◽  
Neutral Hydrogen ◽  
Star Formation History ◽  
Spin Temperature ◽  
Star Forming ◽  
Neutral Gas ◽  
Contemporary Sample ◽  
Formation History ◽  
Radio Band ◽  
Cold Gas

AbstractIt has recently been shown that the abundance of cold neutral gas may follow a similar evolution as the star formation history. This is physically motivated, since stars form out of this component of the neutral gas and if the case, would resolve the long-standing issue that there is a clear disparity between the total abundance of neutral gas and star-forming activity over the history of the Universe. Radio-band 21-cm absorption traces the cold gas and comparison with the Lyman-α absorption, which traces all of the gas, provides a measure of the cold gas fraction, or the spin temperature, Tspin. The recent study has shown that the spin temperature (degenerate with the ratio of the absorber/emitter extent) appears to be anti-correlated with the star formation density, ψ*, with 1/Tspin undergoing a similar steep evolution as ψ* over redshifts of 0 ≲ z ≲ 3, whereas the total neutral hydrogen exhibits little evolution. Above z ∼ 3, where ψ* shows a steep decline with redshift, there are insufficient 21-cm data to determine whether 1/Tspin continues to follow ψ*. Knowing this is paramount in ascertaining whether the cold neutral gas does trace the star formation over the Universe’s history. We explore the feasibility of resolving this with 21-cm observations of the largest contemporary sample of reliable damped Lyman-α absorption systems and conclude that, while today’s largest radio interferometers can reach the required sensitivity at z ≲ 3.5, the Square Kilometre Array is required to probe higher redshifts.

scholarly journals ALMA CO observations of a giant molecular cloud in M 33: Evidence for high-mass star formation triggered by cloud–cloud collisions

2020 ◽  
Author(s):  
Hidetoshi Sano ◽  
Kisetsu Tsuge ◽  
Kazuki Tokuda ◽  
Kazuyuki Muraoka ◽  
Kengo Tachihara ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Line Emission ◽  
High Mass ◽  
H Ii Regions ◽  
Mass Star ◽  
Star Forming ◽  
Spatially Resolved ◽  
Giant Molecular Cloud

Abstract We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M 33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M 33 using 12CO(J = 2–1), 13CO(J = 2–1), and C18O(J = 2–1) line emission at a spatial resolution of ∼2 pc. There are two individual molecular clouds with a systematic velocity difference of ∼6 km s−1. Three continuum sources representing up to ∼10 high-mass stars with spectral types of B0V–O7.5V are embedded within the densest parts of molecular clouds bright in the C18O(J = 2–1) line emission. The two molecular clouds show a complementary spatial distribution with a spatial displacement of ∼6.2 pc, and show a V-shaped structure in the position–velocity diagram. These observational features traced by CO and its isotopes are consistent with those in high-mass star-forming regions created by cloud–cloud collisions in the Galactic and Magellanic Cloud H ii regions. Our new finding in M 33 indicates that cloud–cloud collision is a promising process for triggering high-mass star formation in the Local Group.

scholarly journals The [C ii]–SFR correlation in dwarf galaxies across cosmic time

2020 ◽  
Vol 492 (2) ◽  
pp. 2818-2827 ◽  
Author(s):  
Alessandro Lupi ◽  
Stefano Bovino
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Formation Rate ◽  
Cosmic Time ◽  
Theoretical Models ◽  
Large Scatter ◽  
Star Forming ◽  
Spatially Resolved ◽  
Star Forming Regions ◽  
Neutral Gas

ABSTRACT Current galaxy observations suggest that a roughly linear correlation exists between the [C ii] emission and the star formation rate, either as spatially resolved or integrated quantities. Observationally, this correlation seems to be independent of metallicity, but the very large scatter does not allow to properly assess whether this is true. On the other hand, theoretical models tend to suggest a metallicity dependence of the correlation. In this study, we investigate the metallicity evolution of the correlation via a high-resolution zoom-in cosmological simulation of a dwarf galaxy employing state-of-the-art sub-grid modelling for gas cooling, star formation, and stellar feedback, and that self-consistently evolves the abundances of metal elements out of equilibrium. Our results suggest that the correlation should evolve with metallicity, in agreement with theoretical predictions, but also that this evolution can be hardly detected in observations, because of the large scatter. We also find that most of the [C ii] emission is associated with neutral gas at low-intermediate densities, whereas the highest emissivity is produced by the densest regions around star-forming regions.

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