CHANG-ES XXXI—A Decade of CHANG-ES: What We Have Learned from Radio Observations of Edge-on Galaxies

Irwin, Judith; Beck, Rainer; Cook, Tanden; Dettmar, Ralf-Jürgen; English, Jayanne; Heesen, Volker; Henriksen, Richard; Jiang, Yan; Li, Jiang-Tao; Lu, Li-Yuan; Mele, Crystal; Müller, Ancla; Murphy, Eric; Porter, Troy; Rand, Richard; Skeggs, Nathan; Stein, Michael; Stein, Yelena; Stil, Jeroen; Strong, Andrew; Walterbos, Rene; Wang, Q. Daniel; Wiegert, Theresa; Yang, Yang

doi:10.3390/galaxies12030022

Galaxies

2024

DOI: 10.3390/galaxies12030022

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CHANG-ES XXXI—A Decade of CHANG-ES: What We Have Learned from Radio Observations of Edge-on Galaxies

Judith Irwin,

Rainer Beck,

Tanden Cook

et al.

Abstract: CHANG-ES (Continuum Halos in Nearby Galaxies—an EVLA Survey) is an ambitious project to target 35 nearby disk galaxies that are edge-on to the line of sight. The orientation permits both the disk and halo regions to be studied. The observations were initially at 1.5 GHz (L-band) and 6.0 GHz (C-band) in a variety of VLA array configurations, and in all four Stokes parameters, which allowed for spatially resolved images in total intensity plus polarization. The inclusion of polarization is unique to an edge-on g… Show more

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Cited by 4 publications

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Chang-Es

Heesen,

Wiegert,

Irwin

et al. 2024

A&A

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Cosmic rays may be dynamically very important in driving large-scale galactic winds. Edge-on galaxies give us an outsider's view of radio haloes, and of their extra-planar cosmic-ray electrons and magnetic fields. We present a new radio continuum imaging study of the nearby edge-on galaxy NGC\,4217. We examine the distribution of extra-planar cosmic rays and magnetic fields. We observed it with both the Jansky Very Large Array (JVLA) in the $S$ band (2--4\,GHz) and the LOw Frequency ARray (LOFAR) at 144\,MHz. We measured vertical intensity profiles and exponential scale heights. We re-imaged both the JVLA and LOFAR data at matched angular resolution in order to measure radio spectral indices between 144\,MHz and 3\,GHz. Confusing point-like sources were subtracted prior to imaging. We then fitted intensity profiles with cosmic-ray electron advection models, using an isothermal wind model that is driven by a combination of pressure from the hot gas and cosmic rays. We discover a large-scale radio halo on the north-western side of the galactic disc. The morphology is reminiscent of a bubble extending up to 20\,kpc from the disc. We find spectral ageing in the bubble, which allowed us to measure the advection speeds of the cosmic-ray electrons, which accelerate from 300 to $600\ $. Assuming energy equipartition between the cosmic rays and the magnetic field, we estimate the bubble may have been inflated by a modest 10\,<!PCT!> of the kinetic energy injected by supernovae over its dynamical timescale of 35\,Myr. While no active galactic nucleus (AGN) has been detected, such activity in the recent past cannot be ruled out. Non-thermal bubbles with sizes of tens of kiloparsecs may be a ubiquitous feature of star-forming galaxies, and if so this would demonstrate the influence of feedback. Determining possible contributions by AGN feedback will require deeper observations.

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Chang-Es

Heesen,

Wiegert,

Irwin

et al. 2024

A&A

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eDIG-CHANGES

Lu,

Li,

Vargas

et al. 2024

A&A

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The kinematic information of the extraplanar diffuse ionized gas (eDIG) around galaxies provides clues to the origin of the gas. The eDIG-CHANGES project studies the physical and kinematic properties of the eDIG around the CHANG-ES sample of nearby edge-on disk galaxies. We use a novel multi-slit narrow-band spectroscopy technique to obtain the spatial distribution of the spectral properties of the ionized gas around NGC 891, which is often regarded as an analogue of the Milky Way. We developed specific data reduction procedures for the multi-slit narrow-band spectroscopy data taken with the MDM 2.4m telescope. The data presented in this paper cover the Halpha and N II emission lines. The eDIG traced by the Halpha and N II lines shows an obvious asymmetric morphology, being brighter in the northeastern part of the galactic disk and extending a few kiloparsecs above and below the disk. Global variations in the N II /Halpha line ratio suggest additional heating mechanisms for the eDIG at large heights beyond photoionization. We also construct position-velocity (PV) diagrams of the eDIG based on our optical multi-slit spectroscopy data and compare them to similar PV diagrams constructed with the H I data. The dynamics of the two gas phases are generally consistent with each other. Modelling the rotation curves at different heights from the galactic mid-plane suggests a vertical negative gradient in turnover radius and maximum rotation velocity, with magnitudes of approximately $3 kpc kpc^ $ and $22-25 km s^ kpc^ $, respectively. Our measured vertical gradients of the rotation curve parameters suggest significant differential rotation of the ionized gas in the halo, often referred to as the lagging eDIG. Systematic study of the lagging eDIG, using the multi-slit narrow-band spectroscopy technique developed in our eDIG-CHANGES project, will help us to better understand the dynamics of the ionized gas in the halo.

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Radio Continuum Halos of Seven Nearby Large Galaxies Using uGMRT

Manna,

Roy,

Baug

2024

ApJ

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We present the results of deep radio observations of seven nearby large galaxies observed using the upgraded Giant Metrewave Radio Telescope (uGMRT) 0.3–0.5 GHz receivers with an angular resolution of ∼10″. The achieved sensitivities of these observations range from ≈15 to 50 μJy beam−1, which is a factor of ≈3–4 lower than the previous observations at these frequencies. For two galaxies (NGC 3344 and NGC 3627) with moderate inclination angles, significant diffuse emissions are seen for the first time. The detected radio halos in the vertical direction are significantly larger in our 0.4 GHz maps compared to the observations at ∼1.5 GHz for four nearly edge-on galaxies—NGC 3623, NGC 4096, NGC 4594, and NGC 4631. For these four galaxies, significantly larger halos are also detected along the galaxy disk. For NGC 3623 and NGC 4594, we could detect elongated radio disks that were not seen before. We also present new uGMRT images of NGC 3344 and NGC 3623 at 1.3 GHz and a new VLA image of NGC 3627 at 1.5 GHz. We fitted an exponential function to the flux densities along different cross-cuts and found a significantly wider distribution at the 0.4 GHz uGMRT images compared to the high-frequency images at ∼1.5 GHz. Using maps at 0.144, 0.4, and ∼1.5 GHz, we made spectral index maps of the seven sample galaxies and found a steepening of the spectrum up to a value of ∼−1.5 in the halo regions of the galaxies.

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CHANG-ES XXXI—A Decade of CHANG-ES: What We Have Learned from Radio Observations of Edge-on Galaxies

Cited by 4 publications

References 75 publications

Chang-Es

Chang-Es

eDIG-CHANGES

Radio Continuum Halos of Seven Nearby Large Galaxies Using uGMRT

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