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DOE OSTI2023

A giant umbrella-like stellar stream around the tidal ring galaxy NGC 922

Tidal ring galaxies (TRGs) are rarely observed in the local universe due to their intrinsically transient nature. The tidal ring structures are the result of strong interactions between gas-rich stellar disks and smaller galactic systems, and do not last longer than ~500 Myr. Therefore, these are perfect scenarios in which to look for the debris of recently accreted dwarf galactic systems. Our goal is to study the low surface brightness stellar structures around the TRG NGC 922 and to revise the hypothesis of its formation in light of these new data. We present new deep images of the TRG NGC 922 and its surroundings from the DESI Legacy survey data and from our observations with an amateur telescope. These observations are compared with results from high-resolution N-body simulations that were designed to reproduce an alternative formation scenario for this peculiar galaxy. Our new observations unveil that the low surface brightness stellar tidal structures around NGC 922 are much more complex than reported in previous works. In particular, the formerly detected tidal spike-like structure at the north-east of the central galaxy disk is not connected with the dwarf companion galaxy PGC 3080368, which has been suggested as the intruder triggering the ring formation of NGC 922. The deep images reveal that this tidal structure mainly has a fainter giant umbrella-like shape, and thus it was formed from the tidal disruption of a different satellite. Using the broad-band g, r, and z DESI LS images, we measured the photometric properties of this stellar stream, estimating a total absolute magnitude in the r band of M r = -17.0 ± 0.03 mag and a total stellar mass for the stream of between 6.9 and 8.5×10 8 M ⊙ . We performed a set of N-body simulations to reproduce the observed NGC922-intruder interaction, suggesting a new scenario for the formation of its tidal ring from the infall of a gas-rich satellite around 150 Myr ago. Finally, our deep images also reveal a tidal shell around the dwarf galaxy PGC 3080368, a possible fossil of a recent merger with a smaller satellite, which may suggest it is in its first infall towards NGC 922.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Searching for Mg ii absorbers in and around galaxy clusters

ABSTRACT To study environmental effects on the circumgalactic medium (CGM), we use the samples of redMaPPer galaxy clusters, background quasars, and cluster galaxies from the Sloan Digital Sky Survey (SDSS). With ∼82 000 quasar spectra, we detect 197 Mg ii absorbers in and around the clusters. The detection rate per quasar is 2.7 ± 0.7 times higher inside the clusters than outside the clusters, indicating that Mg ii absorbers are relatively abundant in clusters. However, when considering the galaxy number density, the absorber-to-galaxy ratio is rather low inside the clusters. If we assume that Mg ii absorbers are mainly contributed by the CGM of massive star-forming galaxies, a typical halo size of cluster galaxies is smaller than that of field galaxies by 30 ± 10 per cent. This finding supports that galaxy haloes can be truncated by interaction with the host cluster.

Lee, Jong Chul↗

DOE OSTI2023

An Observed Transition of Galaxy Spins on Void Surfaces

In linear theory, the galaxy angular momentum vectors that originate from initial tidal interactions with surrounding matter distribution intrinsically develop perpendicular alignments with the directions of maximum matter compression, regardless of galaxy mass. In simulations, however, galaxy spins exhibit parallel alignments in the mass range lower than a certain threshold, which depends on redshift, web type, and background cosmology. We show that the observed three-dimensional spins of the spiral galaxies located on the void surfaces from the Sloan Digital Sky Survey indeed transit from perpendicular to parallel alignments with the directions toward the nearest void centers at the threshold zone, 9.51 $\leqslant$ log[M th,$\star$ /(h -1 M ⊙ )] $\leqslant$ 10.03. This study presents the first direct observational evidence for the occurrence of mass-dependent spin transition of real galaxies with respect to non-filamentary structures of the cosmic web, opening a way to constrain the initial conditions of the early universe by measuring the spin transition threshold.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1988

Compact radio cores in three Seyfert galaxies - High resolution studies of Mkn 3, Mkn 231, and Mkn 463

The small-scale morphologies of Mkn 231 and Mkn 463 have been investigated using the European VLBI Network (EVN) at 1.6 GHz and the VLA at 15 and 22 GHz. Mkn 3 has been studied using the EVN at 1.4 and 1.6 GHz. All of the galaxies have a substantial fraction of their core radio flux in linear or elongated structures, typically tens of parsecs in extent. Agreement between the parsec- and kiloparsec-scale position angles of continuum radio emission suggests collimated outflow from the galaxy centers that continues over several orders of magnitude in scale. Supernova rates of order one hundred per year on scales of tens of parsecs are required to explain the nuclear radio emission as the result of bursts of star formation. The luminosities, small extents, and linear morphologies of the radio sources all support the idea that the nuclear radio sources are energized by active galactic nuclei and therefore support the more general picture of Seyfert galaxy nuclei being low-luminosity quasars. All of the galaxies appear to have undergone violent interactions in the recent past.

Neff, S. G.↗

NASA NTRS1990

The infrared continuum spectrum of x ray illuminated molecular gas

In starburst galaxies, active galaxies, and the mysterious ultraluminous infrared galaxies, x rays are likely to interact with molecular gas and dust, thereby inducing infrared emission. X ray heated thermal dust will emit the IR continuum, and x ray photoelectrons will excite an IR emission-line spectrum. Here, researchers model the IR continuum emission characteristic of some selected x ray spectral fluxes, in particular the x ray bremsstrahlung characteristic of supernova and stellar wind bubble shocks in dense media and the power law spectra characteristic of active galactic nuclei. These models are part of a larger project to determine the complete IR spectra, lines plus continuum, of x ray sources embedded in molecular gas. They modeled the thermal emission from grains by calculating a grain temperature/size/composition distribution function, f(T,a,Comp.), which accounts for temperature fluctuations by averaging over all grain thermal histories. In determining the grain thermal distribution, researchers account for both direct grain heating (by x ray absorption and subsequent electron energy deposition) and indirect grain heating (by absorption of the UV emission stimulated by non-thermal photo- and Auger electrons in the gas phase). We let the grain size distribution be proportional to a(exp -3.5), and they consider two types of grain composition: graphites, which we assume to be pure carbon, and silicates, which contain all other depleted heavy elements. They derive the grain composition distribution function from solar abundances and interstellar depletion data.

Voit, G. Mark↗

NASA NTRS1991

A 21 centimeter line survey of a region around four outer galaxy open clusters

To investigate the role of atomic gas in the interaction of massive stars with the interstellar medium, a 21 cm survey was made of a region surrounding four young, outer Galaxy open clusters, NGC 281, 433, 436, and 457. A rectangular area ranging in Galactic longitude from 115 to 133 deg, and in latitude from -10 to -1 deg, was observed with the NRAO 140 foot telescope. Most of this region was fully sampled, resulting in spatial resolution equal to the telescope's 21 arcmin beamwidth. The data are presented as longitude-latitude and latitude-velocity contour maps. A catalog of atomic gas features (e.g., clouds, filaments, and shells) is given.

Leisawitz, David↗

DOE OSTI2024

Self-interacting Dark Matter Interpretation of Crater II

Abstract The satellite galaxy Crater II of the Milky Way is extremely cold and exceptionally diffuse. These unusual properties are challenging to understand in the standard model of cold dark matter. We use controlled N -body simulations to investigate the formation of Crater II in self-interacting dark matter (SIDM), where dark matter particles can scatter and thermalize. Taking the orbit motivated by the measurements from Gaia Early Data Release 3, we show a strong self-interacting cross section per particle mass of 60 cm 2 g −1 is favored for Crater II. The simulated SIDM halo, with a 1 kpc core, leads to both a low stellar velocity dispersion and a large half-light radius for Crater II. These characteristics remain robust regardless of the initial stellar distribution.

Astronomy & Astrophysics↗

NASA NTRS2020

A Catalog of Emission-line Galaxies from the Faint Infrared Grism Survey: Studying Environmental Influence on Star Formation

We present a catalog of 208 0.3 < z < 2.1 emission-line galaxies (ELGs) selected from 1D slitless spectroscopy obtained using Hubble's WFC3 G102 grism, as part of the Faint Infrared Grism Survey. We identify ELG candidates by searching for significant peaks in all continuum-subtracted G102 spectra and, where possible, confirm candidates by identifying consistent emission lines in other available spectra or with published spectroscopic redshifts. We provide derived emission-line fluxes and errors, redshifts, and equivalent widths for Hα λ6563, [O iii] λλ4959, 5007, and [O ii] λ3727 emission lines, for ELGs down to AB(F105W) >28 and >10^(−17) erg/ sq. cms line flux. We use the resulting line catalog to investigate a possible relationship between line emission and a galaxy's environment. We use seventh-nearest-neighbor distances to investigate the typical surroundings of ELGs compared to non-ELGs, and we find that [O iii] emitters are preferentially found at intermediate galaxy densities near galaxy groups. We characterize these ELGs in terms of the galaxy specific star formation rate (SFR) versus stellar mass and find no significant influence of environment on that relation. We calculate SFRs and find no dependence of SFR on local galaxy surface density for 0.3 < z < 0.8 Hα emitters and for 0.8 < z < 1.3 [O iii] emitters. We find similar rates of close-pair interaction between ELGs and non-ELGs. For galaxy surface densities Σ ≤ 30 Mp/sq.c, we find no consistent effect of environment on star formation.

John Pharo↗

NASA NTRS1991

Peculiar morphologies of four IRAS galaxies

Optical and radio data that reveal the peculiar morphologies of four IRAS galaxies are discussed. NGC 1620 is shown to have an off-center arclike structure of 3 kpc radius that may be the largest supernova-blown bubble known. UGC 2982 is an ongoing merger of two gas-rich galaxies. It is shown that the UGC 3004/3005 pair is not interacting despite the proximity of its components. UGC 3004 is a regular barred spiral galaxy. A second nucleus in the edge-on system UGC 3005 suggests a recent merger. Finally, IRAS 23385 + 0300 is one of the most infrared-luminous galaxies known.

Chaboyer, Brian↗

NASA NTRS1992

Dark matter, long-range forces, and large-scale structure

If the dark matter in galaxies and clusters is nonbaryonic, it can interact with additional long-range fields that are invisible to experimental tests of the equivalence principle. We discuss the astrophysical and cosmological implications of a long-range force coupled only to the dark matter and find rather tight constraints on its strength. If the force is repulsive (attractive), the masses of galaxy groups and clusters (and the mean density of the universe inferred from them) have been systematically underestimated (overestimated). We explore the consequent effects on the two-point correlation function, large-scale velocity flows, and microwave background anisotropies, for models with initial scale-invariant adiabatic perturbations and cold dark matter.

Gradwohl, Ben-Ami↗

DOE OSTI2022

Galaxy pairs in the Sloan Digital Sky Survey – XV. Properties of ionized outflows

ABSTRACT Powerful outflows are thought to play a critical role in galaxy evolution and black hole growth. We present the first large-scale systematic study of ionized outflows in paired galaxies and post-mergers compared to a robust control sample of isolated galaxies. We isolate the impact of the merger environment to determine if outflow properties depend on merger stage. Our sample contains ∼4000 paired galaxies and ∼250 post-mergers in the local universe (0.02 ≤ z ≤ 0.2) from the Sloan Digital Sky Survey Data Release 7 (SDSS DR 7) matched in stellar mass, redshift, local density of galaxies, and [O iii] λ5007 luminosity to a control sample of isolated galaxies. By fitting the [O iii] λ5007 line, we find ionized outflows in ∼15 per cent of our entire sample. Outflows are much rarer in star-forming galaxies compared to active galactic nuclei (AGNs), and outflow incidence and velocity increase with [O iii] λ5007 luminosity. Outflow incidence is significantly elevated in the optical + mid-infrared selected AGN compared to purely optical AGN; over 60 per cent show outflows at the highest luminosities ($L_{\mathrm{[OIII]~\lambda 5007}}\, \gtrsim$ 1042 erg s−1), suggesting mid-infrared AGN selection favours galaxies with powerful outflows, at least for higher [O iii] λ5007 luminosities. However, we find no statistically significant difference in outflow incidence, velocity, and luminosity in mergers compared to isolated galaxies, and there is no dependence on merger stage. Therefore, while interactions are predicted to drive gas inflows and subsequently trigger nuclear star formation and accretion activity, when the power source of the outflow is controlled for, the merging environment has no further impact on the large-scale ionized outflows as traced by [O iii] λ5007.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1981

The interstellar medium and galactic structure

High energy gamma rays are produced by the interaction of cosmic rays with the interstellar matter in the galaxy. By combining the gamma ray information with radio data, a picture of the galaxy is presented with regard to the general structure and the effects of cosmic ray pressure. The interaction processes and galactic matter distribution are discussed. Galactic cosmic ray distribution and current gamma ray results are reported.

Source record↗

NASA NTRS1990

A multi-wavelength study of the peculiar galaxy NGC 2976

Researchers are currently studying NGC 2976 at many wavelengths to investigate the extent to which an interaction with M81 may have affected the star formation history of this galaxy. Here, researchers present observations of NGC 2976 made at 50 microns with the high resolution (CPC) instrument onboard Infrared Astronomy Satellite (IRAS) at 21-cm (both HI line and radio continuum) with the Westerbork Synthesis Radio Telescope (WSRT) and in the H alpha line with the Kitt Peak National Observatory (KPNO) 36 inch telescope. The far infrared emission is not centrally peaked as in other spirals (e.g., Wainscoat et al. 1987), but has obvious intensity peaks near the ends of the disk. The ionized gas as inferred from the H alpha observations, is largely confined to two large, symmetrically placed emission regions near the ends of the disk. Finally, the HI and 21-cm radio continuum emission also exhibit this strongly double-peaked structure. At all of the above wavelengths the emission peaks are roughly coincident and lie approx. 1.2 minutes to the NW and approx. 1.1 minutes to the SE of the optical center of this galaxy.

Tacconi, L. J.↗

DOE OSTI2026

Evidence for Environmental Stripping in the Coma Cluster

The stability and longevity of globular clusters (GCs) make them effective tracers of the dynamical histories of galaxies in cluster environments. We construct a catalog of 23,351 GC candidates in the Coma Cluster using imaging from the Hubble Space Telescope Advanced Camera for Surveys. We cross-match galaxy data from the SIMBAD, NASA/IPAC Extragalactic Database, and Sloan Digital Sky Survey archives to construct a galaxy sample and model their GC populations using the GC specific frequency. We find several galaxies with significantly smaller GC populations than expected from their luminosities, consistent with either tidal stripping or intrinsically low formation efficiencies. We analyze annular and Voronoi GC radial profiles of the two brightest cluster galaxies (BCGs), NGC 4874 and NGC 4889, as well as other Coma galaxies. A two-dimensional Voronoi density mapping reveals GC populations with marked deficits compared to our modeled expectations, including galaxies in proximity to the BCGs (e.g., IC 3998, NGC 4875, and NGC 4876) and others distributed across Coma (e.g., NGC 4908, NGC 4883, and IC 4042). Azimuthal symmetry testing suggests past dynamical interactions may have truncated GC systems in some galaxies, while intrinsic deficits are probable in others (e.g., IC 3973, IC 3976, IC 4040, and IC 4045). Our results show that GC deficits exist in several Coma galaxies and that the two-dimensional density structure reveals environmental signatures, with asymmetry statistics consistent with directional stripping. These findings highlight GC populations as powerful probes of environmental processing and the dynamical histories of galaxies in dense cluster environments.

Pomeroy, Richard T. [University of Texas Rio Grand↗

DOE OSTI2022

SDSS IV MaNGA - star-formation driven biconical outflows in face-on galaxies

ABSTRACT We find 132 face-on and low inclination galaxies with central star formation driven biconical gas outflows (FSFB) in the SDSS MaNGA (Mapping Nearby Galaxies at APO) survey. The FSFB galaxies show either double peaked or broadened emission line profiles at their centres. The peak and maximum outflow velocities are 58 and 212 km s−1, respectively. The gas velocity dispersion reveals a mild dependence on the central star formation surface density compatible with models of gas dispersion powered by the Jeans instability in gas clumps or by gas turbulence dissipation. We estimate the gas outflow rate and conclude that the central gas depletion time does not depend on galactic mass. In turn, the ratio of the gas outflow rate to the gas consumption rate by the star formation is low in massive galaxies and high in low mass objects, while the star formation is a more rapid process of the gas consumption. We compare properties of the FSFB galaxies with a control sample of 375 comparison galaxies and find that the FSFB objects have high central concentration of star formation and also younger central stellar population with respect to their periphery. We analysed the environment of the galaxies and identified nearby satellites and elements of low surface brightness structure. We see that many tidal-enhanced features that can be assigned to early and intermediate stages of galactic interaction are much more frequent in the FSFB galaxies with respect to the comparison sample. We conclude that the gas should be replenished via the accretion from small satellites.

Bizyaev, D. (ORCID:000000023601133X)↗

DOE OSTI2024

Scrutinizing the isotropic gamma-ray background in search of dark matter

The isotropic gamma-ray background (IGRB), measured by the Fermi Large Area Telescope, is the result of several classes of extragalactic astrophysical sources. Those sources include blazars, start-forming galaxies and radio galaxies. Also, ultrahigh-energy cosmic rays interacting with the infrared background contribute to the isotropic background. Using information from Fermi’s gamma-ray sources catalog and the results of dedicated studies of these classes of sources, from observations at the infrared and radio, we model their contribution to the IGRB. In addition to conventional astrophysical sources, dark matter may be a component of the IGRB. We combine our model of conventional astrophysical sources and of dark matter annihilation in distant galaxies, marginalizing over relevant uncertainties, to derive constraints on the dark matter annihilation cross section, from the measured IGRB. In calculating the contribution from dark matter we include the flux from extragalactic halos and their substructure and also the subdominant contribution from the Milky Way’s halo at high galactic latitudes. The resulting constraints are competitive with the strongest current constraints from the dwarf spheroidal galaxies. Under certain dark matter assumptions, we also find an indication for a small excess flux in the isotropic background. Here, our results are consistent with the gamma-ray excess at GeV energies toward the galactic center.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

WALLABY pre-pilot survey: two dark clouds in the vicinity of NGC 1395

ABSTRACT We present the Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pre-pilot observations of two ‘dark’ H i sources (with H i masses of a few times 108 $\rm {M}_\odot$ and no known stellar counterpart) that reside within 363 kpc of NGC 1395, the most massive early-type galaxy in the Eridanus group of galaxies. We investigate whether these ‘dark’ H i sources have resulted from past tidal interactions or whether they are an extreme class of low surface brightness galaxies. Our results suggest that both scenarios are possible, and not mutually exclusive. The two ‘dark’ H i sources are compact, reside in relative isolation, and are more than 159 kpc away from their nearest H i-rich galaxy neighbour. Regardless of origin, the H i sizes and masses of both ‘dark’ H i sources are consistent with the H i size–mass relationship that is found in nearby low-mass galaxies, supporting the possibility that these H i sources are an extreme class of low surface brightness galaxies. We identified three analogues of candidate primordial ‘dark’ H i galaxies within the TNG100 cosmological, hydrodynamic simulation. All three model analogues are dark matter dominated, have assembled most of their mass 12–13 Gyr ago, and have not experienced much evolution until cluster infall 1–2 Gyr ago. Our WALLABY pre-pilot science results suggest that the upcoming large-area H i surveys will have a significant impact on our understanding of low surface brightness galaxies and the physical processes that shape them.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

The Signatures of Self-interacting Dark Matter and Subhalo Disruption on Cluster Substructure

The abundance, distribution, and inner structure of satellites of galaxy clusters can be sensitive probes of the properties of dark matter. We run 30 cosmological zoom-in simulations with self-interacting dark matter (SIDM), with a velocity-dependent cross section, to study the properties of subhalos within cluster-mass hosts. We find that the abundance of subhalos that survive in the SIDM simulations are suppressed relative to their cold dark matter (CDM) counterparts. Once the population of disrupted subhalos—which may host orphan galaxies—is taken into account, satellite galaxy populations in CDM and SIDM models can be reconciled. However, even in this case, the inner structures of subhalos are significantly different in the two dark matter models. We study the feasibility of using the weak-lensing signal from the subhalo density profiles to distinguish between the cold and self-interacting dark matter while accounting for the potential contribution of orphan galaxies. We find that the effects of self-interactions on the density profile of subhalos can appear degenerate with subhalo disruption in CDM, when orphans are accounted for. With current error bars from the Subaru Hyper Suprime-Cam Strategic Program, we find that subhalos in the outskirts of clusters (where disruption is less prevalent) can be used to constrain dark matter physics. In the future, the Vera C. Rubin Observatory Legacy Survey of Space and Time will give precise measurements of the weak-lensing profile and can be used to constrain σ $_{T}$/m at the ∼1 cm$^{2}$ g$^{−1}$ level at v ∼ 2000 km s$^{−1}$.

79 ASTRONOMY AND ASTROPHYSICS↗