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The Ly-alpha absorption spectrum of the highest redshift quasars indicates that they are surrounded by giant HII regions, a few Mpc in size. The neutral gas around these HII regions should emit 21cm radiation in excess of the Cosmic…

Astrophysics · Physics 2009-11-10 Stuart Wyithe , Abraham Loeb

Observations of intergalactic neutral hydrogen can provide a wealth of information about structure and galaxy formation, potentially tracing accretion and feedback processes on Mpc scales. Below a column density of NHI ~ 10^19 cm-2, the…

Cosmology and Nongalactic Astrophysics · Physics 2015-05-13 Attila Popping , Romeel Dave , Robert Braun , Benjamin D. Oppenheimer

Absorption-line measurements of the circumgalactic medium (CGM) display a highly non-uniform distribution of lower ionization state species accompanied by more widespread higher ionization state material. This suggests that the CGM is a…

Astrophysics of Galaxies · Physics 2022-03-14 Edward Buie , Evan Scannapieco , G. Mark Voit

Aims. We aim to study the far-infrared radio correlation (FIRC) at 150 MHz in the local Universe (at a median redshift z~0:05) and improve the use of the rest-frame 150-MHz luminosity, L150, as a star-formation rate (SFR) tracer, which is…

Context. The HI distribution at high Galactic latitudes is found to be filamentary and closely related to the far infrared (FIR) in caustics with coherent velocity structures. These structures trace the orientation of the magnetic field…

Astrophysics of Galaxies · Physics 2025-02-04 P. M. W. Kalberla

We examine observational characteristics of multi-phase turbulent flows in the diffuse interstellar medium (ISM) using a synthetic radiation field of atomic and molecular lines. We consider the multi-phase ISM which is formed by thermal…

Astrophysics · Physics 2008-11-26 M. Yamada , H. Koyama , K. Omukai , S. Inutsuka

Based on multi-frequency radio polarization survey datasets, we investigate the spectral characteristics of the Galactic interstellar medium (ISM) using the polarization frequency analysis (PFA) method, referred to as polarization variance.…

High Energy Astrophysical Phenomena · Physics 2026-03-19 Ya-Wen Xiao , Jian-Fu Zhang , Alex Lazarian

We present cosmological ($30-400$ Mpc) distributions of neutral hydrogen (HI) in the inter-galactic medium (IGM) traced by Ly$\alpha$ Emitters (LAEs) and QSOs at $z=2.1-2.5$, selected with the data of the on-going Hobby-Eberly Telescope…

Using the latest upper limits on the 21-cm power spectrum at $z\approx9.1$ from the Low Frequency Array (LOFAR), we explore regions of parameter space which are inconsistent with the data. We use 21CMMC, a Monte Carlo Markov Chain sampler…

Far-infrared (FIR) and mid-infrared (MIR) fine-structure lines (FSLs) provide key diagnostics of physical conditions in the interstellar medium (ISM). Building on empirical relations established in our previous work, we use photoionization…

Astrophysics of Galaxies · Physics 2025-07-17 Bo Peng , Amit Vishwas , Cody Lamarche , Gordon Stacey , Catie Ball , Christopher Rooney , Thomas Nikola , Carl Ferkinhoff

In soft X-rays, the Monogem ring is an object with a diameter of 25{\deg} located in the Galactic anti-centre. It is believed to be a faint, evolved, local supernova remnant. The ring is also visible in the far-ultraviolet, and a few…

Astrophysics of Galaxies · Physics 2020-09-23 Wolfgang Reich , Patricia Reich , Xiaohui Sun

We suggest that large HI holes observed in the interstellar medium (ISM) of galaxies such as the Large Magellanic Cloud (LMC) and Holmberg II (Ho II, DDO 50, UGC 4305) can form as the combined result of turbulence coupled to thermal and…

Astrophysics · Physics 2009-11-10 Sami Dib , Andreas Burkert

We characterize Galactic dust filaments by correlating BICEP/Keck and Planck data with polarization templates based on neutral hydrogen (H I) observations. Dust polarization is important for both our understanding of astrophysical processes…

Observations of the EoR with the 21-cm hyperfine emission of neutral hydrogen (HI) promise to open an entirely new window onto the formation of the first stars, galaxies and accreting black holes. In order to characterize the weak 21-cm…

Cosmology and Nongalactic Astrophysics · Physics 2015-08-06 Abhik Ghosh , L. V. E. Koopmans , Emma Chapman , Vibor Jelic

We use three-dimensional numerical hydrodynamic simulations of the turbulent, multiphase atomic interstellar medium (ISM) to construct and analyze synthetic HI 21 cm emission and absorption lines. Our analysis provides detailed tests of 21…

Astrophysics of Galaxies · Physics 2015-06-19 Chang-Goo Kim , Eve C. Ostriker , Woong-Tae Kim

The formation of molecular gas in interstellar clouds is a slow process, but is enhanced by gas compression. Magnetohydrodynamic (MHD) waves create compressed quasiperiodic linear structures, referred to as striations. Striations are…

Astrophysics of Galaxies · Physics 2023-05-10 R. Skalidis , K. Gkimisi , K. Tassis , G. V. Panopoulou , V. Pelgrims , A. Tritsis , P. F. Goldsmith

Observations of far-infrared (FIR) and submillimeter (SMM) polarized emission are used to study magnetic fields and dust grains in dense regions of the interstellar medium (ISM). These observations place constraints on models of molecular…

Astrophysics · Physics 2009-03-19 John E. Vaillancourt

Context. Neutral atomic hydrogen (HI) absorption lines can be used to probe the cold neutral medium (CNM) at high Galactic latitudes. Cold HI with a significant optical depth from the GASKAP-HI survey is found to be located predominantly if…

Astrophysics of Galaxies · Physics 2025-11-26 P. M. W. Kalberla

We consider the scenario of a magnetic field orthogonal to a front separating two media of different temperatures and densities, such as cold and warm interstellar gas, in a 2-D plane-parallel geometry. A linear stability analysis is…

Astrophysics of Galaxies · Physics 2011-02-11 Jennifer M. Stone , Ellen G. Zweibel

We discuss the feasibility of the detection of the 21cm forest in the diffuse IGM with the radio telescope LOFAR. The optical depth to the 21cm line has been derived using simulations of reionization which include detailed radiative…