scholarly journals Theoretical Modeling of the Diffuse Emission of Gamma Rays from Extreme Regions of Star Formation: The Case of ARP 220

2004 ◽  
Vol 617 (2) ◽  
pp. 966-986 ◽  
Author(s):  
Diego F. Torres
Keyword(s):  
Star Formation ◽  
Gamma Rays ◽  
Theoretical Modeling ◽  
Diffuse Emission

scholarly journals An uncertainty principle for star formation – IV. On the nature and filtering of diffuse emission

2019 ◽  
Vol 488 (2) ◽  
pp. 2800-2824 ◽  
Author(s):  
Alexander P S Hygate ◽  
J M Diederik Kruijssen ◽  
Mélanie Chevance ◽  
Andreas Schruba ◽  
Daniel T Haydon ◽  
...  
Keyword(s):  
Star Formation ◽  
Compact Star ◽  
Critical Length ◽  
Electromagnetic Spectrum ◽  
H Ii Regions ◽  
Diffuse Emission ◽  
Star Forming ◽  
Star Forming Regions ◽  
Compact Component ◽  
Astronomical Images

Abstract Diffuse emission is observed in galaxies in many tracers across the electromagnetic spectrum, including tracers of star formation, such as H α and ultraviolet (UV), and tracers of gas mass, such as carbon monoxide (CO) transition lines and the 21-cm line of atomic hydrogen (H i). Its treatment is key to extracting meaningful information from observations such as cloud-scale star formation rates. Finally, studying diffuse emission can reveal information about the physical processes taking place in the interstellar medium, such as chemical transitions and the nature of stellar feedback (through the photon escape fraction). We present a physically motivated method for decomposing astronomical images containing both diffuse emission and compact regions of interest, such as H ii regions or molecular clouds, into diffuse and compact component images through filtering in Fourier space. We have previously presented a statistical method for constraining the evolutionary timeline of star formation and mean separation length between compact star-forming regions with galaxy-scale observations. We demonstrate how these measurements are biased by the presence of diffuse emission in tracer maps and that by using the mean separation length as a critical length-scale to separate diffuse emission from compact emission, we are able to remove its biasing effect. Furthermore, this method provides, without the need for interferometry or ancillary spectral data, a measurement of the diffuse emission fraction in input tracer maps and decomposed diffuse and compact emission maps for further analysis.

scholarly journals Radio morphology of southern narrow-line Seyfert 1 galaxies with Very Large Array observations*

2020 ◽  
Vol 498 (1) ◽  
pp. 1278-1297
Author(s):  
S Chen ◽  
E Järvelä ◽  
L Crepaldi ◽  
M Zhou ◽  
S Ciroi ◽  
...  
Keyword(s):  
Star Formation ◽  
Radio Emission ◽  
Large Mass ◽  
Large Array ◽  
Narrow Line ◽  
Diffuse Emission ◽  
Jets And Outflows ◽  
Very Large Array ◽  
Radio Jets ◽  
New Radio

ABSTRACT We present the results of new radio observations carried out with the Karl G. Jansky Very Large Array C-configuration at 5.5 GHz for a sample of southern narrow-line Seyfert 1 galaxies (NLS1s). This work increases the number of known radio-detected NLS1s in the Southern hemisphere, and confirms that the radio emission of NLS1s is mainly concentrated in a central region at kpc-scale and only a few sources show diffuse emission. In radio-quiet NLS1s, the radio luminosity tends to be higher in steep-spectrum sources and be lower in flat-spectrum sources, which is opposite to radio-loud NLS1s. This may be because the radio emission of steep NLS1s is dominated by misaligned jets, active galactic nucleus driven outflows, or star formation superposing on a compact core. Instead the radio emission of flat NLS1s may be produced by a central core that has not yet developed radio jets and outflows. We discover new NLS1s harbouring kpc-scale radio jets and confirm that a powerful jet does not require a large-mass black hole to be generated. We also find sources dominated by star formation. These NLS1s could be new candidates in investigating the radio emission of different mechanisms.

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 Kinematic study of the molecular gas associated with two cometary globules in Sh2−236

2020 ◽  
Vol 633 ◽  
pp. A27
Author(s):  
M. E. Ortega ◽  
S. Paron ◽  
M. B. Areal ◽  
M. Rubio
Keyword(s):  
Star Formation ◽  
Radial Velocity ◽  
Angular Resolution ◽  
Optical Data ◽  
Molecular Gas ◽  
Diffuse Emission ◽  
B Stars ◽  
Kinematic Study ◽  
Star Formation Activity ◽  
Ubiquitous Presence

Aims. Cometary globules, dense molecular gas structures exposed to UV radiation, are found inside H II regions. Understanding the nature and origin of these structures through a kinematic study of the molecular gas could be useful to advance in our knowledge of the interplay between radiation and molecular gas. Methods. Using the Atacama Submillimeter Telescope Experiment (Chile), we carried out molecular observations toward two cometary globules (Sim129 and Sim130) in the H II region Sh2−236. We mapped two regions of about 1′ × 1′ with the 12CO J = 3−2 and HCO+ J = 4−3 lines. Additionally, we carried out two single pointings with the C2H N = 4–3, HNC, and HCN J = 4−3 transitions. The angular resolution was about 22′′. We combined our molecular observations with public infrared and optical data to analyze the distribution and kinematics of the molecular gas. Results. We find kinematic signatures of infalling gas in the 12CO J = 3−2 and C2H N = 4−3 spectra toward Sim 129. We detect HCO+, HCN, and HNC J = 4−3 only toward Sim 130. The HCN/HNC integrated ratio of about three found in Sim 130 suggests that the possible star-formation activity inside this globule has not yet ionized the gas. The location of the NVSS source 052255+33315, which peaks toward the brightest border of the globule, supports this scenario. The non-detection of these molecules toward Sim 129 could be due to the radiation field arising from the star-formation activity inside this globule. The ubiquitous presence of the C2H molecule toward Sim 129 and Sim 130 evidences the action of the nearby O-B stars irradiating the external layer of both globules. Based on the mid-infrared 5.8 μm emission, we identify two new structures: (1) a region of diffuse emission (R1) located, in projection, in front of the head of Sim 129 and (2) a pillar-like feature (P1) placed besides Sim 130. Based on the 12CO J = 3−2 transition, we find molecular gas associated with Sim 129, Sim 130, R1, and P1 at radial velocities of −1.5, −11, +10, and +4 km s−1, respectively. Therefore, while Sim 129 and P1 are located at the far side of the shell, Sim 130 is placed at the near side, consistent with earlier results. Finally, the molecular gas related to R1 exhibits a radial velocity that differs in more than 11 km s−1 with the radial velocity of S129, which suggests that while S129 is located at the far side of the expanding shell, R1 would be placed well beyond.

scholarly journals The MUSE Extremely Deep Field: The cosmic web in emission at high redshift

2021 ◽  
Vol 647 ◽  
pp. A107
Author(s):  
R. Bacon ◽  
D. Mary ◽  
T. Garel ◽  
J. Blaizot ◽  
M. Maseda ◽  
...  
Keyword(s):  
Star Formation ◽  
Surface Brightness ◽  
Luminosity Function ◽  
Filling Factor ◽  
High Redshift ◽  
Large Population ◽  
Diffuse Emission ◽  
Average Surface ◽  
High Significance ◽  
Circumgalactic Medium

We report the discovery of diffuse extended Lyα emission from redshift 3.1 to 4.5, tracing cosmic web filaments on scales of 2.5−4 cMpc. These structures have been observed in overdensities of Lyα emitters in the MUSE Extremely Deep Field, a 140 h deep MUSE observation located in the Hubble Ultra-Deep Field. Among the 22 overdense regions identified, five are likely to harbor very extended Lyα emission at high significance with an average surface brightness of 5 × 10−20 erg s−1 cm−2 arcsec−2. Remarkably, 70% of the total Lyα luminosity from these filaments comes from beyond the circumgalactic medium of any identified Lyα emitter. Fluorescent Lyα emission powered by the cosmic UV background can only account for less than 34% of this emission at z ≈ 3 and for not more than 10% at higher redshift. We find that the bulk of this diffuse emission can be reproduced by the unresolved Lyα emission of a large population of ultra low-luminosity Lyα emitters (< 1040 erg s−1), provided that the faint end of the Lyα luminosity function is steep (α ⪅ −1.8), it extends down to luminosities lower than 1038 − 1037 erg s−1, and the clustering of these Lyα emitters is significant (filling factor < 1/6). If these Lyα emitters are powered by star formation, then this implies their luminosity function needs to extend down to star formation rates < 10−4 M⊙ yr−1. These observations provide the first detection of the cosmic web in Lyα emission in typical filamentary environments and the first observational clue indicating the existence of a large population of ultra low-luminosity Lyα emitters at high redshift.

Diffuse Gamma Rays of Galactic and Extragalactic Origin: Preliminary Results from EGRET

1996 ◽  
Vol 168 ◽  
pp. 279-288
Author(s):  
P. Sreekumar ◽  
D.A. Kniffen
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
Emission Model ◽  
Diffuse Emission ◽  
Interstellar Gas ◽  
Cosmic Ray Interactions ◽  
Galactic Model ◽  
Energy Gamma

The all-sky survey in high energy gamma rays (E&gt;30 MeV) carried out by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory provides for the first time an opportunity to examine in detail diffuse gamma-ray emission of extra-galactic origin. The observed diffuse emission at high galactic latitudes is generally assumed to have a galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation, in addition to an isotropic component presumably of extragalactic origin. The galactic component can be estimated from a model of the interstellar medium and cosmic-ray distribution. Since the derived extragalactic spectrum depends very much on the success of our galactic model, the consistency of the galactic diffuse emission model is examined both spectrally and spatially with existing EGRET observations. In conjunction with this model, EGRET observations of the high latitude emission are used to examine the flux and spectrum of the residual extragalactic emission. This residual emission could be either truly diffuse in origin or could arise from accumulated emission from unresolved sources particularly in the light of EGRET observations showing the presence of numerous gamma-ray bright active galactic nuclei.

scholarly journals Kiso Hα Imaging Observations of Nearby Galaxies

1998 ◽  
Vol 15 (1) ◽  
pp. 149-151
Author(s):  
T. Hasegawa ◽  
S. Sakamoto ◽  
S. Nishiura ◽  
Y. Ohyama ◽  
Y. Sofue
Keyword(s):  
Star Formation ◽  
Compact Group ◽  
Spiral Galaxy ◽  
Clear Correlation ◽  
Nuclear Region ◽  
Diffuse Emission ◽  
Schmidt Telescope ◽  
Group System ◽  
Nearby Galaxies ◽  
Formation Efficiency

AbstractWe report Hα imaging observations of nearby galaxies with the Kiso Schmidt telescope. For spiral galaxy NGC 628, we found no clear correlation between Hα and CO intensities, and we discuss the star formation efficiency of this galaxy. No nuclear Hα emission in this galaxy was detected. This is consistent with spectroscopic observations which indicate that the nuclear region is in the post starburst phase. We also describe the Hα image of Hickson's compact group 92 in which diffuse emission is detected extending within the group system.

scholarly journals INTEGRALSPI All‐Sky View in Soft Gamma Rays: A Study of Point‐Source and Galactic Diffuse Emission

2008 ◽  
Vol 679 (2) ◽  
pp. 1315-1326 ◽  
Author(s):  
L. Bouchet ◽  
E. Jourdain ◽  
J.‐P. Roques ◽  
A. Strong ◽  
R. Diehl ◽  
...  
Keyword(s):  
Point Source ◽  
Gamma Rays ◽  
Diffuse Emission

scholarly journals GAMMA RAYS FROM STAR FORMATION IN CLUSTERS OF GALAXIES

2012 ◽  
Vol 755 (2) ◽  
pp. 117 ◽  
Author(s):  
Emma M. Storm ◽  
Tesla E. Jeltema ◽  
Stefano Profumo
Keyword(s):  
Star Formation ◽  
Gamma Rays ◽  
Clusters Of Galaxies
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