scholarly journals Galactic centre star formation writ large in gamma-rays

2011 ◽  
Author(s):  
Roland Crocker
Keyword(s):  
Star Formation ◽  
Gamma Rays ◽  
Galactic Centre

scholarly journals A new distance to the Brick, the dense molecular cloud G0.253+0.016

2021 ◽  
Vol 502 (1) ◽  
pp. 1246-1252
Author(s):  
M Zoccali ◽  
E Valenti ◽  
F Surot ◽  
O A Gonzalez ◽  
A Renzini ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Near Infrared ◽  
Formation Rate ◽  
Dynamical Evolution ◽  
Galactic Centre ◽  
The Galaxy ◽  
Centre Region ◽  
Order Of Magnitude ◽  
Red Clump

ABSTRACT We analyse the near-infrared colour–magnitude diagram of a field including the giant molecular cloud G0.253+0.016 (a.k.a. The Brick) observed at high spatial resolution, with HAWK-I@VLT. The distribution of red clump stars in a line of sight crossing the cloud, compared with that in a direction just beside it, and not crossing it, allow us to measure the distance of the cloud from the Sun to be 7.20, with a statistical uncertainty of ±0.16 and a systematic error of ±0.20 kpc. This is significantly closer than what is generally assumed, i.e. that the cloud belongs to the near side of the central molecular zone, at 60 pc from the Galactic centre. This assumption was based on dynamical models of the central molecular zone, observationally constrained uniquely by the radial velocity of this and other clouds. Determining the true position of the Brick cloud is relevant because this is the densest cloud of the Galaxy not showing any ongoing star formation. This puts the cloud off by one order of magnitude from the Kennicutt–Schmidt relation between the density of the dense gas and the star formation rate. Several explanations have been proposed for this absence of star formation, most of them based on the dynamical evolution of this and other clouds, within the Galactic centre region. Our result emphasizes the need to include constraints coming from stellar observations in the interpretation of our Galaxy’s central molecular zone.

scholarly journals Heart of darkness: the influence of galactic dynamics on quenching star formation in galaxy spheroids

2020 ◽  
Vol 495 (1) ◽  
pp. 199-223 ◽  
Author(s):  
Jindra Gensior ◽  
J M Diederik Kruijssen ◽  
Benjamin W Keller
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Formation Rate ◽  
Free Fall ◽  
Galactic Centre ◽  
Causal Connection ◽  
Isolated Galaxies ◽  
Stellar Halo ◽  
Hydrodynamical Simulations ◽  
The Impact

ABSTRACT Quenched galaxies are often observed to contain a strong bulge component. The key question is whether this reflects a causal connection – can star formation be quenched dynamically by bulges or the spheroids of early-type galaxies? We systematically investigate the impact of these morphological components on star formation, by performing a suite of hydrodynamical simulations of isolated galaxies containing a spheroid. We vary the bulge mass and scale radius, while the total initial stellar, halo, and gas mass are kept constant, with a gas fraction of 5 per cent. In addition, we consider two different sub-grid star formation prescriptions. The first follows most simulations in the literature by assuming a constant star formation efficiency per free-fall time, whereas in the second model it depends on the gas virial parameter, following high-resolution simulations of turbulent fragmentation. Across all simulations, central spheroids increase the gas velocity dispersion towards the galactic centre. This increases the gravitational stability of the gas disc, suppresses fragmentation and star formation, and results in galaxies hosting extremely smooth and quiescent gas discs that fall below the galaxy main sequence. These effects amplify when using the more sophisticated, dynamics-dependent star formation model. Finally, we discover a pronounced relation between the central stellar surface density and star formation rate (SFR), such that the most bulge-dominated galaxies show the strongest deviation from the main sequence. We conclude that the SFR of galaxies is not only set by the balance between accretion and feedback, but carries a (sometimes dominant) dependence on the gravitational potential.

scholarly journals MAGMO: polarimetry of 1720-MHz OH masers towards southern star-forming regions

2020 ◽  
Vol 493 (1) ◽  
pp. 199-233 ◽  
Author(s):  
C S Ogbodo ◽  
J A Green ◽  
J R Dawson ◽  
S L Breen ◽  
S A Mao ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Ground State ◽  
Supernova Remnants ◽  
Galactic Centre ◽  
Galactic Magnetic Field ◽  
Field Orientation ◽  
Star Forming ◽  
Star Forming Regions ◽  
Methanol Masers

ABSTRACT From targeted observations of ground-state hydroxyl (OH) masers towards 702 Methanol Multibeam survey 6.7-GHz methanol masers, in the Galactic longitude range from 186° through the Galactic Centre to 20°, made as part of the ‘MAGMO’ (Mapping the Galactic Magnetic field through OH masers) project, we present the physical and polarization properties of the 1720-MHz OH maser transition, including the identification of Zeeman pairs. We present 10 new and 23 previously catalogued 1720-MHz OH maser sources detected towards star-forming regions (SFRs). In addition, we also detected 16 1720-MHz OH masers associated with supernova remnants and two sites of diffuse OH emission. Towards the 33 star formation masers, we identify 44 Zeeman pairs, implying magnetic field strengths ranging from −11.4 to +13.2 mG, and a median magnetic field strength of |BLOS| ∼ 6 mG. With limited statistics, we present the in situ magnetic field orientation of the masers and the Galactic magnetic field distribution revealed by the 1720-MHz transition. We also examine the association statistics of 1720-MHz OH SFR masers with other ground-state OH masers, excited-state OH masers, class I and class II methanol masers, and water masers, and compare maser positions with mid-infrared images of the parent SFRs. Of the 33 1720-MHz star formation masers, 10 are offset from their central exciting sources, and appear to be associated with outflow activity.

scholarly journals Evolution of the Extragalactic Infrared-to-Ultraviolet Background and Gamma-Ray Attenuation

2001 ◽  
Vol 204 ◽  
pp. 153-153
Author(s):  
T. M. Kneiske ◽  
K. Mannheim
Keyword(s):  
Star Formation ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Background Radiation ◽  
Formation Rate ◽  
Cosmological Parameters ◽  
Cosmic Background Radiation ◽  
Initial Mass Function ◽  
Order Unity ◽  
Gamma Ray Attenuation

We describe a model for the evolution of the cosmic background radiation field from infrared to ultraviolet wavelengths tuned to observations of star formation and including the effects of reprocessing by dust and gas. With this model, we can compute the attenuation of gamma rays from extragalactic sources. The attenuation length for the vast majority of extragalactic gamma-ray sources (blazars and gamma-ray bursts at redshifts of order unity) depends on the evolving optical-to-ultraviolet background, whereas gamma-ray attenuation measurements of nearby sources-such as Mrk 501 probe the infrared background. We focus on the cosmological aspects of the model and discuss the effects of changing cosmological parameters, star formation rate, initial mass function, and dust opacity on the resulting gamma-ray attenuation. A plausible choice of parameters leads to fair agreement between our model in the infrared and the observed attenuation of gamma rays from Mrk 501.

scholarly journals Extinction in the 11.2 µm PAH band and the low L11.2/LIR in ULIRGs

2020 ◽  
Vol 497 (4) ◽  
pp. 4614-4625
Author(s):  
Antonio Hernán-Caballero ◽  
Henrik W W Spoon ◽  
Almudena Alonso-Herrero ◽  
Evanthia Hatziminaoglou ◽  
Georgios E Magdis ◽  
...  
Keyword(s):  
Star Formation ◽  
Equivalent Width ◽  
Flux Ratio ◽  
Width Ratio ◽  
Galactic Centre ◽  
Star Forming ◽  
Intrinsic Flux ◽  
Star Formation In Galaxies ◽  
The Impact ◽  
Small Dispersion

ABSTRACT We present a method for recovering the intrinsic (extinction-corrected) luminosity of the 11.2 μm PAH band in galaxy spectra. Using 105 high S/N Spitzer/IRS spectra of star-forming galaxies, we show that the equivalent width ratio of the 12.7 and 11.2 μm PAH bands is independent on the optical depth (τ), with small dispersion (∼5 per cent) indicative of a nearly constant intrinsic flux ratio Rint = (f12.7/f11.2)int = 0.377 ± 0.020. Conversely, the observed flux ratio, Robs = (f12.7/f11.2)obs, strongly correlates with the silicate strength (Ssil) confirming that differences in Robs reflect variation in τ. The relation between Robs and Ssil reproduces predictions for the Galactic Centre extinction law but disagrees with other laws. We calibrate the total extinction affecting the 11.2 μm PAH from Robs, which we apply to another sample of 215 galaxies with accurate measurements of the total infrared luminosity (LIR) to investigate the impact of extinction on L11.2/LIR. Correlation between L11.2/LIR and Robs independently on LIR suggests that increased extinction explains the well-known decrease in the average L11.2/LIR at high LIR. The extinction-corrected L11.2 is proportional to LIR in the range LIR = 109–1013 L⊙. These results consolidate L11.2 as a robust tracer of star formation in galaxies.

scholarly journals Cosmic ray models of the ridge-like excess of gamma rays in the Galactic Centre

2015 ◽  
Vol 451 (2) ◽  
pp. 1833-1847 ◽  
Author(s):  
Oscar Macias ◽  
Chris Gordon ◽  
Roland M. Crocker ◽  
Stefano Profumo
Keyword(s):  
Gamma Rays ◽  
Cosmic Ray ◽  
Galactic Centre

scholarly journals Star formation at the Galactic Centre: coevolution of multiple young stellar discs

2019 ◽  
Vol 490 (4) ◽  
pp. 5820-5831 ◽  
Author(s):  
Alessandra Mastrobuono-Battisti ◽  
Hagai B Perets ◽  
Alessia Gualandris ◽  
Nadine Neumayer ◽  
Anna C Sippel
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Direct Evidence ◽  
Galactic Nuclei ◽  
Galactic Centre ◽  
Stellar Clusters ◽  
Stellar Disc ◽  
The Galaxy ◽  
Kinematic Properties

ABSTRACT Studies of the Galactic Centre suggest that in situ star formation may have given rise to the observed stellar population near the central supermassive black hole (SMBH). Direct evidence for a recent starburst is provided by the currently observed young stellar disc (2–7 Myr) in the central 0.5 pc of the Galaxy. This result suggests that star formation in galactic nuclei may occur close to the SMBH and produce initially flattened stellar discs. Here, we explore the possible build-up and evolution of nuclear stellar clusters near SMBHs through in situ star formation producing stellar discs similar to those observed in the Galactic Centre and other nuclei. We use N-body simulations to model the evolution of multiple young stellar discs and explore the potential observable signatures imprinted by such processes. Each of the five simulated discs is evolved for 100 Myr before the next one is introduced in the system. We find that populations born at different epochs show different morphologies and kinematics. Older and presumably more metal-poor populations are more relaxed and extended, while younger populations show a larger amount of rotation and flattening. We conclude that star formation in central discs can reproduce the observed properties of multiple stellar populations in galactic nuclei differing in age, metallicity, and kinematic properties.

scholarly journals The link between solenoidal turbulence and slow star formation in G0.253+0.016

2016 ◽  
Vol 11 (S322) ◽  
pp. 123-128 ◽  
Author(s):  
C. Federrath ◽  
J. M. Rathborne ◽  
S. N. Longmore ◽  
J. M. D. Kruijssen ◽  
J. Bally ◽  
...  
Keyword(s):  
Star Formation ◽  
Mach Number ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Dust Emission ◽  
Volume Density ◽  
Galactic Centre ◽  
Galactic Disc ◽  
Density Variance

AbstractStar formation in the Galactic disc is primarily controlled by gravity, turbulence, and magnetic fields. It is not clear that this also applies to star formation near the Galactic Centre. Here we determine the turbulence and star formation in the CMZ cloud G0.253+0.016. Using maps of 3 mm dust emission and HNCO intensity-weighted velocity obtained with ALMA, we measure the volume-density variance σρ /ρ 0=1.3±0.5 and turbulent Mach number $\mathcal{M}$ = 11±3. Combining these with turbulence simulations to constrain the plasma β = 0.34±0.35, we reconstruct the turbulence driving parameter b=0.22±0.12 in G0.253+0.016. This low value of b indicates solenoidal (divergence-free) driving of the turbulence in G0.253+0.016. By contrast, typical clouds in the Milky Way disc and spiral arms have a significant compressive (curl-free) driving component (b > 0.4). We speculate that shear causes the solenoidal driving in G0.253+0.016 and show that this may reduce the star formation rate by a factor of 7 compared to nearby clouds.

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