Photometric and spectroscopic studies of star-forming regions within Wolf–Rayet galaxies

Karthick, Chrisphin; López-Sánchez, Á. R.; Sahu, D. K.; Sanwal, B. B.; Bisht, Shuchi

doi:10.1093/mnras/stt2301

Cited by 15 publications

(20 citation statements)

References 114 publications

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“…2). It is described as a disturbed galaxy with asymmetric spiral arms (Karthick et al 2014) with indications for a starburst superwind (Hoopes et al 1999). Hence, the inclination may be smaller than 85 • and we cannot fully trust our scale height values for this galaxy.…”

Section: Frequency Dependence Of Radio Scale Heightsmentioning

confidence: 89%

Chang-Es

Krause

Irwin

Wiegert

et al. 2018

A&A

169

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Aim. The vertical halo scale height is a crucial parameter to understand the transport of cosmic-ray electrons (CRE) and their energy loss mechanisms in spiral galaxies. Until now, the radio scale height could only be determined for a few edge-on galaxies because of missing sensitivity at high resolution.Methods. We developed a sophisticated method for the scale height determination of edge-on galaxies. With this we determined the scale heights and radial scale lengths for a sample of 13 galaxies from the CHANG-ES radio continuum survey in two frequency bands.Results. The sample average values for the radio scale heights of the halo are 1.1 ± 0.3 kpc in C-band and 1.4 ± 0.7 kpc in L-band. From the frequency dependence analysis of the halo scale heights we found that the wind velocities (estimated using the adiabatic loss time) are above the escape velocity. We found that the halo scale heights increase linearly with the radio diameters. In order to exclude the diameter dependence, we defined a normalized scale height h˜ which is quite similar for all sample galaxies at both frequency bands and does not depend on the star formation rate or the magnetic field strength. However, h˜ shows a tight anticorrelation with the mass surface density.Conclusions. The sample galaxies with smaller scale lengths are more spherical in the radio emission, while those with larger scale lengths are flatter. The radio scale height depends mainly on the radio diameter of the galaxy. The sample galaxies are consistent with an escape-dominated radio halo with convective cosmic ray propagation, indicating that galactic winds are a widespread phenomenon in spiral galaxies. While a higher star formation rate or star formation surface density does not lead to a higher wind velocity, we found for the first time observational evidence of a gravitational deceleration of CRE outflow, e.g. a lowering of the wind velocity from the galactic disk.

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Section: Frequency Dependence Of Radio Scale Heightsmentioning

confidence: 89%

Chang-Es

Krause

Irwin

Wiegert

et al. 2018

A&A

169

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“…We also do not consider Wolf-Rayet stars, planetary nebulae or high-mass XRBs to be viable explanations for the observed [Fe X]λ6374 emission in our sample. While both Wolf-Rayet stars and planetary nebulae can produce coronal-line emission, they do not present [Fe X]λ6374 emission (Schaerer & Stasińska 1999;Pottasch et al 2009;Zhang et al 2012), and no [Fe X] emission has been reported in Wolf-Rayet galaxies (e.g., Karthick et al 2014;Fernandes et al 2004). Meanwhile, the Be star-neutron star X-ray binary, which is the largest sub-group of high-mass XRBs, does not produce any observable optical coronal emission lines (e.g., Coe et al 2021).…”

Section: Wolf-rayet Stars Planetary Nebulae and Hmxrbsmentioning

confidence: 99%

A Sample of Massive Black Holes in Dwarf Galaxies Detected via [Fe X] Coronal Line Emission: Active Galactic Nuclei and/or Tidal Disruption Events

Molina,

Reines,

Latimer

et al. 2021

Preprint

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The massive black hole (BH) population in dwarf galaxies (M BH 10 5 M ) can provide strong constraints on the origin of BH seeds. However, traditional optical searches for active galactic nuclei (AGNs) only reliably detect high-accretion, relatively high-mass BHs in dwarf galaxies with low amounts of star formation, leaving a large portion of the overall BH population in dwarf galaxies relatively unexplored. Here, we present a sample of 81 dwarf galaxies (M ≤ 3 × 10 9 M ) with detectable [Fe X]λ6374 coronal line emission indicative of accretion onto massive BHs, only two of which were previously identified as optical AGNs. We analyze optical spectroscopy from the Sloan Digital Sky Survey and find [Fe X]λ6374 luminosities in the range L [F ex] ≈ 10 36 -10 39 erg s −1 , with a median value of 1.6 × 10 38 erg s −1 . The [Fe X]λ6374 luminosities are generally much too high to be produced by stellar sources, including luminous Type IIn supernovae (SNe). Moreover, based on known SNe rates, we expect at most 8 Type IIn SNe in our sample. On the other hand, the [Fe X]λ6374 luminosities are consistent with accretion onto massive BHs from AGNs or tidal disruption events (TDEs). We find additional indicators of BH accretion in some cases using other emission line diagnostics, optical variability, X-ray and radio emission (or some combination of these). However, many of the galaxies in our sample only have evidence for a massive BH based on their [Fe X]λ6374 luminosities. This work highlights the power of coronal line emission to find BHs in dwarf galaxies missed by other selection techniques and to probe the BH population in bluer, lower mass dwarf galaxies.

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“…At high metallicity, a steep increase in N/O ratio is believed to be due to increased secondary production and partly also due to selective depletion of oxygen in dust grains (e.g., Kobulnicky & Skillman 1998;Pilyugin et al 2003;Mollá et al 2006;Izotov et al 2006a). Some WR galaxies also show excess nitrogen in the range of 0.25 − 0.85 dex in the relation between log(N/O) and 12+log(O/H) over all the metallicity regimes (Kobulnicky et al 1997;Pustilnik et al 2004;López-Sánchez et al 2007;Brinchmann et al 2008;López-Sánchez & Esteban 2010b;Jaiswal & Omar 2013;Karthick et al 2014). The excess of nitrogen in WR galaxies is attributed to nitrogen ejection in luminosity-driven stellar winds of WR stars.…”

Section: α-Elements To Oxygen Ratiosmentioning

confidence: 99%

Optical spectroscopy of star-forming regions in dwarf Wolf–Rayet galaxies

Paswan

Omar

Jaiswal

2018

Monthly Notices of the Royal Astronomical Society

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We present here spatially-resolved optical spectroscopic observations of four nearby dwarf Wolf-Rayet (WR) galaxies. The ages of the most recent starburst events in these galaxies are found between 3 and 10 Myr. The gas-phase metallicities [12+log(O/H)] for the spatially-resolved star-forming regions are derived using several indicators. The star-forming regions within the galaxies are found chemically homogeneous within the uncertainties in the estimates. Nitrogen-enrichment as expected in the WR regions is not detected. This implies that metal-enrichment due to supernovae explosions in the most recent star-forming episode is not being detected here. It is suggested that the newly synthesized metals still reside in hot gas-phase. The metals from the previous episodes, cooled by now and well mixed across the whole extent of galaxies, are making galaxies chemically homogeneous with normal N/O ratio. These galaxies are residing in dense environments with galaxy density in the range of 8 − 80 Mpc −3 .

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Photometric and spectroscopic studies of star-forming regions within Wolf–Rayet galaxies

Cited by 15 publications

References 114 publications

Chang-Es

Chang-Es

A Sample of Massive Black Holes in Dwarf Galaxies Detected via [Fe X] Coronal Line Emission: Active Galactic Nuclei and/or Tidal Disruption Events

Optical spectroscopy of star-forming regions in dwarf Wolf–Rayet galaxies

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