We revisit the H i size–mass (
$D_{\rm H\,{\small I}}$
–M
H i
) relation of galaxies with a sample of more than 500 nearby galaxies covering over five orders of magnitude in H i mass and more than 10 ...B-band magnitudes. The relation is remarkably tight with a scatter σ ∼ 0.06 dex, or 14 per cent. The scatter does not change as a function of galaxy luminosity, H i richness or morphological type. The relation is linked to the fact that dwarf and spiral galaxies have a homogeneous radial profile of H i surface density in the outer regions when the radius is normalized by D
H i
. The early-type disc galaxies typically have shallower H i radial profiles, indicating a different gas accretion history. We argue that the process of atomic-to-molecular gas conversion or star formation cannot explain the tightness of the D
H i
–M
H i
relation. This simple relation puts strong constraints on simulation models for galaxy formation.
Aims. The mergers of galaxy clusters are the most energetic events in the Universe after the Big Bang. With the increased availability of multi-object spectroscopy and X-ray data, an ever increasing ...fraction of local clusters are recognised as exhibiting signs of recent or past merging events on various scales. Our goal is to probe how these mergers affect the evolution and content of their member galaxies. We specifically aim to answer the following questions: is the quenching of star formation in merging clusters enhanced when compared with relaxed clusters? Is the quenching preceded by a (short-lived) burst of star formation? Methods. We obtained optical spectroscopy of >400 galaxies in the field of the merging cluster Abell 520. We combine these observations with archival data to obtain a comprehensive picture of the state of star formation in the members of this merging cluster. Finally, we compare these observations with a control sample of ten non-merging clusters at the same redshift from The Arizona Cluster Redshift Survey (ACReS). We split the member galaxies into passive, star forming or recently quenched depending on their spectra. Results. The core of the merger shows a decreased fraction of star forming galaxies compared to clusters in the non-merging sample. This region, dominated by passive galaxies, is extended along the axis of the merger. We find evidence of rapid quenching of the galaxies during the core passage with no signs of a star burst on the time scales of the merger (≲0.4 Gyr). Additionally, we report the tentative discovery of an infalling group along the main filament feeding the merger, currently at ~ 2.5 Mpc from the merger centre. This group contains a high fraction of star forming galaxies as well as approximately two thirds of all the recently quenched galaxies in our survey.
Abstract
We use the single-dish radio telescope Five-hundred meter Aperture Spherical Telescope (FAST) to map the H
i
in the tidally interacting NGC 4631 group with a resolution of 3.′24 (7 kpc), ...reaching a 5
σ
column density limit of 10
17.9
cm
−2
assuming a line width of 20 km s
−1
. Taking the existing interferometric H
i
image from the Hydrogen Accretion in LOcal GAlaxieS project of Westerbork Synthesis Radio Telescope as a reference, we are able to identify and characterize a significant excess of large-scale, low-density, and diffuse H
i
in the group. This diffuse H
i
extends more than 120 kpc across, and accounts for more than one-fourth of the total H
i
detected by FAST in and around the galaxy NGC 4631. In the region of the tidal tails, the diffuse H
i
has a typical column density above 10
19.5
cm
−2
, and is highly turbulent with a velocity dispersion of around 50 km s
−1
. It increases in column density with the dense H
i
, and tends to be associated with the kinematically
hotter
part of the dense H
i
. Through simple modeling, we find that the majority of the diffuse H
i
in the tail region is likely to induce cooling out of the hot intragalactic medium (IGM) instead of evaporating or being radiatively ionized. Given these relations of gas in different phases, the diffuse H
i
may represent a condensing phase of the IGM. Ongoing and past active tidal interactions may have produced the wide-spreading H
i
distribution, and triggered the gas accretion to NGC 4631 through the phase of the diffuse H
i
.
Context. As a result of their relation to massive stars, long-duration gamma-ray bursts (GRBs) allow the pinpointing of star formation in galaxies independent of redshift, dust obscuration, or galaxy ...mass/size, thus providing a unique tool to investigate star formation history over cosmic time. Aims. About half of the optical afterglows of long-duration GRBs are missed owing to dust extinction and are primarily located in the most massive GRB hosts. It is important to investigate the amount of obscured star formation in these GRB host galaxies to understand this bias. Methods. Radio emission of galaxies correlates with star formation, but does not suffer extinction as do the optical star formation estimators. We selected 11 GRB host galaxies with either large stellar mass or large UV-based and optical-based star formation rates (SFRs) and obtained radio observations of these with the Australia Telescope Compact Array and the Karl Jansky Very Large Array. Results. Despite intentionally selecting GRB hosts with expected high SFRs, we do not find any radio emission related to star formation in any of our targets. Our upper limit for GRB 100621A implies that the earlier reported radio detection was due to afterglow emission. We detect radio emission from the position of GRB 020819B, but argue that it is in large part, if not completely, due to afterglow contamination. Conclusions. Half of our sample has radio-derived SFR limits, which are only a factor 2–3 above the optically measured SFRs. This supports other recent studies that the majority of star formation in GRB hosts is not obscured by dust.
Abstract
We built a multiwavelength data set for galaxies from the Local Volume H i Survey (LVHIS), which comprises 82 galaxies. We also select a sub-sample of 10 large galaxies for investigating ...properties in the galactic outskirts. The LVHIS sample covers nearly four orders of magnitude in stellar mass and two orders of magnitude in H i mass fraction (
$f_{\rm {H\,\small {I}}}$
). The radial distribution of H i gas with respect to the stellar disc is correlated with
$f_{\rm {H\,\small {I}}}$
but with a large scatter. We confirm the previously found correlations between the total H i mass and star formation rate (SFR), and between H i surface densities and SFR surface densities beyond R25. However, the former correlation becomes much weaker when the average surface densities rather than total mass or rate are considered, and the latter correlation also becomes much weaker when the effect of stellar mass is removed or controlled. Hence, the link between SFR and H i is intrinsically weak in these regions, consistent with what was found on kiloparsecs scales in the galactic inner regions. We find a strong correlation between the SFR surface density and the stellar mass surface density, which is consistent with the star formation models where the gas is in quasi-equilibrium with the mid-plane pressure. We find no evidence for H i warps to be linked with decreasing star-forming efficiencies.
MeerKAT-16 H i observation of the dIrr galaxy WLM Ianjamasimanana, Roger; Namumba, Brenda; Ramaila, Athanaseus J T ...
Monthly notices of the Royal Astronomical Society,
10/2020, Letnik:
497, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We present observations and models of the kinematics and the distribution of the neutral hydrogen (H i) in the isolated dwarf irregular galaxy, Wolf-Lundmark-Melotte (WLM). We observed WLM ...with the Green Bank Telescope (GBT) and as part of the MeerKAT Early Science Programme, where 16 dishes were available. The H i disc of WLM extends out to a major axis diameter of 30 arcmin (8.5 kpc), and a minor axis diameter of 20 arcmin (5.6 kpc) as measured by the GBT. We use the MeerKAT data to model WLM using the tirific software suite, allowing us to fit different tilted-ring models and select the one that best matches the observation. Our final best-fitting model is a flat disc with a vertical thickness, a constant inclination and dispersion, and a radially varying surface brightness with harmonic distortions. To simulate bar-like motions, we include second-order harmonic distortions in velocity in the tangential and vertical directions. We present a model with only circular motions included and a model with non-circular motions. The latter describes the data better. Overall, the models reproduce the global distribution and the kinematics of the gas, except for some faint emission at the 2σ level. We model the mass distribution of WLM with pseudo-isothermal (ISO) and Navarro–Frenk–White (NFW) dark matter halo models. The NFW and the ISO models fit the derived rotation curves within the formal errors, but with the ISO model giving better reduced chi-square values. The mass distribution in WLM is dominated by dark matter at all radii.
ABSTRACT
Superthin galaxies are bulgeless low-surface brightness galaxies with unusually high major-to-minor axes ratio of the stellar disc, i.e. 10 < a/b < 20. We present Giant Metrewave Radio ...Telescope (GMRT) H i 21cm radio-synthesis observations of FGC 2366, the thinnest galaxy known with a/b = 21.6. Employing the 3D tilted-ring modelling using fully automated TiRiFiC (fat), we determine the structure and kinematics of the H i gas disc, obtaining an asymptotic rotational velocity equal to 100 km s−1 and a total H i mass equal to 109M⊙. Using z-band stellar photometry, we obtain a central surface brightness of 22.8 mag arcsec−2, a disc scale length of 2.6 kpc, and a scale height of 260 pc. Next, we determine the dark matter density profile by constructing a mass model and find that an Navarro–Frenk–White (NFW) dark matter halo best-fits the steeply rising rotation curve. With the above mass inventory in place, we finally construct the dynamical model of the stellar disc of FGC 2366 using the stellar dynamical code ‘agama’. To identify the key physical mechanisms responsible for the superthin vertical structure, we carry out a Principal Component Analysis of the data corresponding to all the relevant dynamical parameters and a/b for a sample of superthin and extremely thin galaxies studied so far. We note that the first two principal components explain 80 per cent of the variation in the data, and the significant contribution is from the compactness of the mass distribution, which is fundamentally responsible for the existence of superthin stellar discs.
Mass models of gas-rich void dwarf galaxies Kurapati, Sushma; Chengalur, Jayaram N; Kamphuis, Peter ...
Monthly notices of the Royal Astronomical Society,
02/2020, Letnik:
491, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We construct mass models of eight gas rich dwarf galaxies that lie in the Lynx–Cancer void. From NFW fits to the dark matter halo profile, we find that the concentration parameters of haloes ...of void dwarf galaxies are similar to those of dwarf galaxies in normal density regions. We also measure the slope of the central dark matter density profiles, obtained by converting the rotation curves derived using 3D (fat) and 2D (ROTCUR) tilted ring fitting routines, into mass densities. We find that the average slope (α = −1.39 ± 0.19), obtained from 3D fitting is consistent with that expected from an NFW profile. On the other hand, the average slope measured using the 2D approach is closer to what would be expected for an isothermal profile. This suggests that systematic effects in velocity field analysis have a significant effect on the slope of the central dark matter density profiles. Given the modest number of galaxies we use for our analysis, it is important to check these results using a larger sample.
Studying the nature of various types of supernovae (SNe) is important for our understanding of stellar evolution. Observations of atomic and molecular gas in the host galaxies of gamma-ray bursts ...(GRBs) and SNe have recently been used to learn about the nature of the explosions themselves and the star formation events during which their progenitors were born. Based on archival data for M 74, which previously has not been investigated in the context of SN positions, we report the gas properties in the environment of the broad-lined type Ic (Ic-BL) SN 2002ap and the type II SNe 2003gd, 2013ej, and 2019krl. The SN 2002ap is located at the end of an off-centre, asymmetric, 55 kpc-long H
I
extension containing 7.5% of the total atomic gas in M 74, interpreted as a signature of external gas accretion. It is the fourth known case of an explosion of a presumably massive star located close to a concentration of atomic gas (after GRBs 980425, 060505, and SN 2009bb). It is unlikely that all these associations are random (at a 3
σ
significance), so the case of SN 2002ap adds to the evidence that the birth of the progenitors of type Ic-BL SNe and GRBs is connected with the accretion of atomic gas from the intergalactic medium. The H
I
extension could come from tidally disrupted companions of M 74, or be a remnant of a galaxy or a gas cloud that accreted entirely from the intragroup medium. The other (type II) SNe in M 74 are located at the outside edge of a spiral arm. This suggests that either their progenitors were born when gas was piling up there or that the SN progenitors moved away from the arm due to their orbital motions. These type II SNe do not seem to be related to gas accretion.
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