scholarly journals The in-situ formation of molecular and warm ionised gas triggered by hot galactic outflows

2021 ◽  
Author(s):  
Philipp Girichidis ◽  
Thorsten Naab ◽  
Stefanie Walch ◽  
Thomas Berlok
Keyword(s):  
Time Scales ◽  
High Redshift ◽  
Field Configuration ◽  
Star Forming ◽  
Molecular Outflows ◽  
Order Of Magnitude ◽  
H2 Formation ◽  
Self Gravity ◽  
The Magnetic Field

Abstract Molecular outflows contributing to the matter cycle of star forming galaxies are now observed in small and large systems at low and high redshift. Their physical origin is still unclear. In most theoretical studies only warm ionised/neutral and hot gas outflowing from the interstellar medium is generated by star formation. We investigate an in-situ H2 formation scenario in the outflow using high-resolution simulations, including non-equilibrium chemistry and self-gravity, of turbulent, warm, and atomic clouds with densities 0.1, 0.5 and 1 cm−3 exposed to a magnetised hot wind. For cloud densities ≳ 0.5 cm−3 a magnetised wind triggers H2 formation before cloud dispersal. Up to 3 per cent of the initial cloud mass can become molecular on ∼10 Myr time scales. The effect is stronger for winds with perpendicular B-fields and intermediate density clouds (nc ∼ 0.5 cm−3). Here H2 formation can be boosted by up to one order of magnitude compared to isolated cooling clouds independent of self-gravity. Self-gravity preserves the densest clouds well past their ∼15 Myr cloud crushing time scales. This model could provide a plausible in-situ origin for the observed molecular gas. All simulations form warm ionised gas, which represents an important observable phase. The amount of warm ionised gas is almost independent of the cloud density but solely depends on the magnetic field configuration in the wind. For low density clouds (0.1 cm−3), up to 60 per cent of the initially atomic cloud mass can become warm and ionised.

scholarly journals The nature of faint radio galaxies at high redshifts

2019 ◽  
Vol 489 (4) ◽  
pp. 5053-5075 ◽  
Author(s):  
A Saxena ◽  
H J A Röttgering ◽  
K J Duncan ◽  
G J Hill ◽  
P N Best ◽  
...  
Keyword(s):  
Near Infrared ◽  
High Redshift ◽  
Radio Galaxies ◽  
Star Forming ◽  
Inverse Compton Scattering ◽  
Inverse Compton ◽  
Order Of Magnitude ◽  
Stellar Masses ◽  
Scattering Losses ◽  
Rule Out

ABSTRACT We present spectra and near-infrared images of a sample of faint radio sources initially selected as promising high-redshift radio galaxy (HzRG) candidates. We have determined redshifts for a total of 13 radio galaxies with redshifts ranging from 0.52 ≤ $z$ ≤ 5.72. Our sample probes radio luminosities that are almost an order of magnitude fainter than previous large samples at the highest redshifts. We use near-infrared photometry for a subsample of these galaxies to calculate stellar masses using simple stellar population models, and find stellar masses to be in the range $10^{10.8} {--}10^{11.7} \, \mathrm{M}_\odot$. We then compare our faint radio galaxies with brighter radio galaxies at $z$ ≥ 2 from the literature. We find that fainter radio galaxies have lower Ly α luminosities and narrower line widths compared to the bright ones, implying photoionization by a weaker active galactic nucleus (AGN). We also rule out the presence of strong shocks in faint HzRGs. The stellar masses determined for faint HzRGs are lower than those observed for brighter ones. We find that faint HzRG population in the redshift range 2–4 forms a bridge between star-forming and narrow-line AGNs, whereas the ones at $z$ > 4 are likely to be dominated by star formation, and may be building up their stellar mass through cold accretion of gas. Finally, we show that the overall redshift evolution of radio sizes at $z$ > 2 is fully compatible with increased inverse Compton scattering losses at high redshifts.

scholarly journals New submillimeter diagnostics of physical properties of ISM in high redshift galaxies

2006 ◽  
Vol 2 (S235) ◽  
pp. 430-430
Author(s):  
Yoichi Tamura ◽  
Kouichiro Nakanishi ◽  
Kotaro Kohno ◽  
Ryohei Kawabe
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
High Redshift ◽  
Formation Rate ◽  
Host Galaxies ◽  
Power Sources ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
Order Of Magnitude ◽  
New Diagnosis

AbstractWe present a new diagnosis method for determining physical properties of star-forming gas in high-z galaxies. In this method, we employed three key observational quantities, [CI], CO, and FIR luminosities, including our new detections of CO J = 4–3 emission from the pure-starburst (non-AGN) submm galaxy SMM J14011+0252 (z = 2.6) and the type-2 AGN IRAS FSC 10214+4724 (z = 2.3) obtained with the Nobeyama Millimeter Array (NMA) at the Nobeyama Radio Observatory. These two sources have extremely high star formation rate, and exhibit strong emission of CO and [CI] 609 μm lines. We determined ISM physical conditions for the two objects and another three high-z quasars in order to investigate the relationship between their ISM and power sources (i.e., massive star formation or AGN). A new PDR analysis (Wolfire et al. 2005, private communication) using CO, [CI], and FIR on five high-z sources provides new evidence that AGN host galaxies harbor denser (log nH ~ 5–6) ISM exposed to stronger far-UV fluxes of log G0 ~ 3.5–4 than the non-AGN submm galaxy. Volume filling factors of the star-forming dense gas in the AGN hosts are an order of magnitude smaller than that of the pure-starburst submm galaxy. This suggests that, in these AGN hosts, dense molecular clouds are dominating the central kpc around AGN, triggering extensive circumnuclear starbursts, and possibly feeding their central supermassive black hole simultaneously.

scholarly journals 8.14. Magnetic fields in star-forming regions of our Galaxy

1998 ◽  
Vol 184 ◽  
pp. 371-372
Author(s):  
B. Hutawarakorn ◽  
R. J. Cohen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Zeeman Splitting ◽  
Theoretical Work ◽  
Field Configuration ◽  
Galactic Magnetic Field ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Magnetic Field

Masers provide a direct way of measuring magnetic fields in star-forming regions. OH ground-state masers at 18 cm wavelength exhibit strong circular polarization due to Zeeman splitting. The implied magnetic field strength is typically a few mG, which is sufficient for the field to be dynamically important, e.g. in channelling the observed bipolar outflows. Moreover there are indications that magnetic fields in maser regions are aligned with the large-scale Galactic magnetic field (Reid & Silverstein 1990), and that bipolar molecular outflows are also aligned with the local Galactic magnetic field (Cohen, Rowland & Blair 1984). Some theoretical work in fact suggests that the magnetic field is intimately connected with the origin of the molecular outflow (e.g. Pudritz & Norman 1983; Uchida & Shibata 1985). It is therefore important to investigate the magnetic field configuration in these regions in as much detail as possible.

scholarly journals The time-scales probed by star formation rate indicators for realistic, bursty star formation histories from the FIRE simulations

2020 ◽  
Author(s):  
José A Flores Velázquez ◽  
Alexander B Gurvich ◽  
Claude-André Faucher-Giguére ◽  
James S Bullock ◽  
Tjitske K Starkenburg ◽  
...  
Keyword(s):  
Star Formation ◽  
Time Scales ◽  
Galaxy Formation ◽  
Time Scale ◽  
High Redshift ◽  
Formation Rate ◽  
Star Forming ◽  
Best Fitting ◽  
Far Ultraviolet ◽  
Star Formation Histories

Abstract Understanding the rate at which stars form is central to studies of galaxy formation. Observationally, the star formation rates (SFRs) of galaxies are measured using the luminosity in different frequency bands, often under the assumption of a time-steady SFR in the recent past. We use star formation histories (SFHs) extracted from cosmological simulations of star-forming galaxies from the FIRE project to analyze the time-scales to which the Hα and far-ultraviolet (FUV) continuum SFR indicators are sensitive. In these simulations, the SFRs are highly time variable for all galaxies at high redshift, and continue to be bursty to z = 0 in dwarf galaxies. When FIRE SFHs are partitioned into their bursty and time-steady phases, the best-fitting FUV time-scale fluctuates from its ∼10 Myr value when the SFR is time-steady to ≳100 Myr immediately following particularly extreme bursts of star formation during the bursty phase. On the other hand, the best-fitting averaging time-scale for Hα is generally insensitive to the SFR variability in the FIRE simulations and remains ∼ 5 Myr at all times. These time-scales are shorter than the 100 Myr and 10 Myr time-scales sometimes assumed in the literature for FUV and Hα, respectively, because while the FUV emission persists for stellar populations older than 100 Myr, the time-dependent luminosities are strongly dominated by younger stars. Our results confirm that the ratio of SFRs inferred using Hα vs. FUV can be used to probe the burstiness of star formation in galaxies.

scholarly journals COLDz: Probing Cosmic Star Formation With Radio Free–Free Emission

2022 ◽  
Vol 924 (2) ◽  
pp. 76
Author(s):  
Hiddo S. B. Algera ◽  
Jacqueline A. Hodge ◽  
Dominik A. Riechers ◽  
Sarah K. Leslie ◽  
Ian Smail ◽  
...  
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Formation Rate ◽  
Radio Spectrum ◽  
Star Formation History ◽  
Starburst Galaxy ◽  
Synchrotron Emission ◽  
Very Large Array ◽  
Star Forming ◽  
Order Of Magnitude

Abstract Radio free–free emission is considered to be one of the most reliable tracers of star formation in galaxies. However, as it constitutes the faintest part of the radio spectrum—being roughly an order of magnitude less luminous than radio synchrotron emission at the GHz frequencies typically targeted in radio surveys—the usage of free–free emission as a star formation rate tracer has mostly remained limited to the local universe. Here, we perform a multifrequency radio stacking analysis using deep Karl G. Jansky Very Large Array observations at 1.4, 3, 5, 10, and 34 GHz in the COSMOS and GOODS-North fields to probe free–free emission in typical galaxies at the peak of cosmic star formation. We find that z ∼ 0.5–3 star-forming galaxies exhibit radio emission at rest-frame frequencies of ∼65–90 GHz that is ∼1.5–2 times fainter than would be expected from a simple combination of free–free and synchrotron emission, as in the prototypical starburst galaxy M82. We interpret this as a deficit in high-frequency synchrotron emission, while the level of free–free emission is as expected from M82. We additionally provide the first constraints on the cosmic star formation history using free–free emission at 0.5 ≲ z ≲ 3, which are in good agreement with more established tracers at high redshift. In the future, deep multifrequency radio surveys will be crucial in order to accurately determine the shape of the radio spectrum of faint star-forming galaxies, and to further establish radio free–free emission as a tracer of high-redshift star formation.

scholarly journals Signatures of interchange reconnection: STEREO, ACE and Hinode observations combined

2009 ◽  
Vol 27 (10) ◽  
pp. 3883-3897 ◽  
Author(s):  
D. Baker ◽  
A. P. Rouillard ◽  
L. van Driel-Gesztelyi ◽  
P. Démoulin ◽  
L. K. Harra ◽  
...  
Keyword(s):  
Electron Flux ◽  
Field Configuration ◽  
Direct Result ◽  
Magnetic Field Configuration ◽  
Closed Loops ◽  
In Situ Data ◽  
Field Lines ◽  
Mass Ejection ◽  
The Magnetic Field

Abstract. Combining STEREO, ACE and Hinode observations has presented an opportunity to follow a filament eruption and coronal mass ejection (CME) on 17 October 2007 from an active region (AR) inside a coronal hole (CH) into the heliosphere. This particular combination of "open" and closed magnetic topologies provides an ideal scenario for interchange reconnection to take place. With Hinode and STEREO data we were able to identify the emergence time and type of structure seen in the in-situ data four days later. On the 21st, ACE observed in-situ the passage of an ICME with "open" magnetic topology. The magnetic field configuration of the source, a mature AR located inside an equatorial CH, has important implications for the solar and interplanetary signatures of the eruption. We interpret the formation of an "anemone" structure of the erupting AR and the passage in-situ of the ICME being disconnected at one leg, as manifested by uni-directional suprathermal electron flux in the ICME, to be a direct result of interchange reconnection between closed loops of the CME originating from the AR and "open" field lines of the surrounding CH.

scholarly journals Stellar masses of giant clumps in CANDELS and simulated galaxies using machine learning

2020 ◽  
Vol 499 (1) ◽  
pp. 814-835
Author(s):  
Marc Huertas-Company ◽  
Yicheng Guo ◽  
Omri Ginzburg ◽  
Christoph T Lee ◽  
Nir Mandelker ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
Gravitational Lensing ◽  
High Redshift ◽  
Mass Function ◽  
Stellar Mass ◽  
Star Forming ◽  
Mixture Density ◽  
Distant Galaxies ◽  
Stellar Masses

ABSTRACT A significant fraction of high redshift star-forming disc galaxies are known to host giant clumps, whose nature and role in galaxy evolution are yet to be understood. In this work, we first present a new method based on neural networks to detect clumps in galaxy images. We use this method to detect clumps in the rest-frame optical and UV images of a complete sample of ∼1500 star forming galaxies at 1 < z < 3 in the CANDELS survey as well as in images from the VELA zoom-in cosmological simulations. We show that observational effects have a dramatic impact on the derived clump properties leading to an overestimation of the clump mass up to a factor of 10, which highlights the importance of fair comparisons between observations and simulations and the limitations of current HST data to study the resolved structure of distant galaxies. After correcting for these effects with a mixture density network, we estimate that the clump stellar mass function follows a power law down to the completeness limit (107 solar masses) with the majority of the clumps being less massive than 109 solar masses. This is in better agreement with recent gravitational lensing based measurements. The simulations explored in this work overall reproduce the shape of the observed clump stellar mass function and clumpy fractions when confronted under the same conditions, although they tend to lie in the lower limit of the confidence intervals of the observations. This agreement suggests that most of the observed clumps are formed in situ.

scholarly journals EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

2019 ◽  
Vol 623 ◽  
pp. A130 ◽  
Author(s):  
G. Surcis ◽  
W. H. T. Vlemmings ◽  
H. J. van Langevelde ◽  
B. Hutawarakorn Kramer ◽  
A. Bartkiewicz
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Massive Star ◽  
Zeeman Splitting ◽  
Limited Sample ◽  
Star Forming ◽  
Molecular Outflows ◽  
Star Forming Regions ◽  
The Magnetic Field

Context. Magnetohydrodynamical simulations show that the magnetic field can drive molecular outflows during the formation of massive protostars. The best probe to observationally measure both the morphology and the strength of this magnetic field at scales of 10–100 au is maser polarization. Aims. We measure the direction of magnetic fields at milliarcsecond resolution around a sample of massive star-forming regions to determine whether there is a relation between the orientation of the magnetic field and of the outflows. In addition, by estimating the magnetic field strength via the Zeeman splitting measurements, the role of magnetic field in the dynamics of the massive star-forming region is investigated. Methods. We selected a flux-limited sample of 31 massive star-forming regions to perform a statistical analysis of the magnetic field properties with respect to the molecular outflows characteristics. We report the linearly and circularly polarized emission of 6.7 GHz CH3OH masers towards seven massive star-forming regions of the total sample with the European VLBI Network. The sources are: G23.44−0.18, G25.83−0.18, G25.71−0.04, G28.31−0.39, G28.83−0.25, G29.96−0.02, and G43.80−0.13. Results. We identified a total of 219 CH3OH maser features, 47 and 2 of which showed linearly and circularly polarized emission, respectively. We measured well-ordered linear polarization vectors around all the massive young stellar objects and Zeeman splitting towards G25.71−0.04 and G28.83−0.25. Thanks to recent theoretical results, we were able to provide lower limits to the magnetic field strength from our Zeeman splitting measurements. Conclusions. We further confirm (based on ∼80% of the total flux-limited sample) that the magnetic field on scales of 10–100 au is preferentially oriented along the outflow axes. The estimated magnetic field strength of |B||| > 61 mG and >21 mG towards G25.71−0.04 and G28.83−0.25, respectively, indicates that it dominates the dynamics of the gas in both regions.

scholarly journals Resolved star formation relations at high redshift from the IRAM PHIBSS program

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Jonathan Freundlich ◽  
Françoise Combes ◽  
Linda Tacconi ◽  
Michael Cooper ◽  
Reinhard Genzel ◽  
...  
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Formation Rate ◽  
Molecular Gas ◽  
Formation Processes ◽  
Massive Galaxies ◽  
Star Forming ◽  
Star Forming Regions ◽  
Order Of Magnitude ◽  
Formation Efficiency

AbstractObserved massive galaxies in the distant Universe form stars at much higher rates than today. High levels of star formation are sustained by a continuous supply of fresh gas and high molecular gas fractions. But after a peak around redshift z=2-3, the star formation rate decreases by an order of magnitude. Is this evolution mostly driven by the available cold gas reservoir, or are the star formation processes qualitatively different near the star formation peak? The Kennicutt-Schmidt relation enables to characterize the star formation efficiency at low and high redshift, but resolved measurements at the scale of the star-forming regions themselves are still challenging at high redshift. Molecular gas observations carried out at the IRAM Plateau de Bure interferometer within the PHIBSS program (Tacconi, Combes et al.) permit us to study the star formation efficiency at sub-galactic scales around z=1.2 and 1.5 for a limited sample of galaxies, and thus help characterize the star formation processes at this epoch. Our results lay in the continuation of the resolved low-redshift measurements, but further studies would be necessary to complement our sample and validate our conclusions.

scholarly journals A comparison of methods for finding magnetic nulls in simulations and in situ observations of space plasmas

2020 ◽  
Vol 644 ◽  
pp. A150
Author(s):  
V. Olshevsky ◽  
D. I. Pontin ◽  
B. Williams ◽  
C. E. Parnell ◽  
H. S. Fu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Configuration ◽  
Space Plasmas ◽  
Index Method ◽  
Stagnation Points ◽  
Poincaré Index ◽  
Spacecraft Data ◽  
Poincare Index ◽  
The Magnetic Field

Context. Magnetic nulls are ubiquitous in space plasmas, and are of interest as sites of localised energy dissipation or magnetic reconnection. As such, a number of methods have been proposed for detecting nulls in both simulation data and in situ spacecraft data from Earth’s magnetosphere. The same methods can be applied to detect stagnation points in flow fields. Aims. In this paper we describe a systematic comparison of different methods for finding magnetic nulls. The Poincaré index method, the first-order Taylor expansion (FOTE) method, and the trilinear method are considered. Methods. We define a magnetic field containing fourteen magnetic nulls whose positions and types are known to arbitrary precision. Furthermore, we applied the selected techniques in order to find and classify those nulls. Two situations are considered: one in which the magnetic field is discretised on a rectangular grid, and the second in which the magnetic field is discretised along synthetic “spacecraft trajectories” within the domain. Results. At present, FOTE and trilinear are the most reliable methods for finding nulls in the spacecraft data and in numerical simulations on Cartesian grids, respectively. The Poincaré index method is suitable for simulations on both tetrahedral and hexahedral meshes. Conclusions. The proposed magnetic field configuration can be used for grading and benchmarking the new and existing tools for finding magnetic nulls and flow stagnation points.

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