Aims. We analyze a MUSE optical integral field spectrum of the star-forming edge-on galaxy IC 1553 in order to study its extraplanar diffuse ionized gas (eDIG) and the processes shaping its disk-halo ...interface. Methods. We extracted the optical emission line properties from the integral field spectrum and generated the commonly used emission line diagnostic diagrams in order to analyze the ionization conditions and the distribution of the eDIG. Furthermore, we performed gravitational potential fitting to investigate the kinematics of a suspected galactic outflow. Results. We find that the eDIG scale height has a maximum value of approximately 1.0 kpc and decreases roughly linearly with the radial distance from the galactic center in projection. The ionization state of the eDIG is not consistent with a pure photoionization scenario and instead requires a significant contribution from shock ionization. This, in addition to the gas kinematics, strongly suggests the presence of a galactic scale outflow, the origin of which lies at least 1.4 kpc away from the galactic center. The inferred shock velocity in the eDIG of approximately 225 km s-1 is comparable to the escape velocity estimated from our potential modelling. The asymmetric distribution of currently star-forming clusters produces a range of different ionization conditions in the eDIG. As a result, the vertical emission line profiles vary quantitatively and qualitatively along the major axis of the galaxy. This analysis illustrates that it is crucial in studies of the eDIG to use observations that take the spatial and kinematical distributions into account, such as those done with integral field units, to form an accurate picture of the relevant physical properties.
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) \HI{} 21cm radio-synthesis observations of FGC 2366, the thinnest galaxy known with \(a/b=21.6\). Employing the 3-D tilted-ring modelling using Fully Automated TiRiFiC (FAT), we determine the structure and kinematics of the \HI{} gas disc, obtaining an asymptotic rotational velocity equal to 100 \kms and a total \HI{} mass equal to 10\(^9 M_{\odot}\). Using \(z\)-band stellar photometry, we obtain a central surface brightness of 22.8 mag \({\rm{arcsec}}^{-2}\), a disc scale length of 2.6 kpc, and a scaleheight of 260 pc. Next, we determine the dark matter density profile by constructing a mass model and find that an 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\(\%\) 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.
We present early results from the ongoing Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) Survey, which is being performed with the Westerbork Synthesis Radio Telescope (WSRT). The HALOGAS Survey aims ...to detect and characterize the cold gas accretion process in nearby spirals, through sensitive observations of neutral hydrogen (Hi) 21-cm line emission. In this contribution, we present an overview of ongoing analyses of several HALOGAS targets.
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 M74, 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 HI extension containing 7.5% of the total atomic gas in M74, 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 3sigma 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 HI extension could come from tidally disrupted companions of M74, or be a remnant of a galaxy or a gas cloud that accreted entirely from the intragroup medium. The other (type II) SNe in M74 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.
We present observations and models of the kinematics and distribution of neutral hydrogen (HI) in the superthin galaxy FGC 1440 with an optical axial ratio \(a/b = 20.4\). Using the Giant Meterwave ...Radio telescope (GMRT), we imaged the galaxy with a spectral resolution of 1.7 \(\rm kms^{-1}\) and a spatial resolution of \(15" \times 13.5"\). We find that FGC 1440 has an asymptotic rotational velocity of 141.8 \(\rm kms^{-1}\) . The structure of the HI disc in FGC 1440 is that of a typical thin disc warped along the line of sight, but we can not rule out the presence of a central thick HI disc. We find that the dark matter halo in FGC 1440 could be modeled by a pseudo-isothermal (PIS) profile with \(\rm R_{c}/ R_{d} <2\), where \(R_{c}\) is the core radius of the PIS halo and \(R_{d}\) the exponential stellar disc scale length. We note that in spite of the unusually large axial ratio of FGC 1440, the ratio of the rotational velocity to stellar vertical velocity dispersion, \(\frac{V_{Rot}}{\sigma_{z}} \sim 5 - 8\), which is comparable to other superthins. Interestingly, unlike previously studied superthin galaxies which are outliers in the \(log_{10}(j_{*}) - log_{10}(M_{*})\) relation for ordinary bulgeless disc galaxies, FGC 1440 is found to comply with the same. The values of \(j\) for the stars, gas and the baryons in FGC 1440 are consistent with those of normal spiral galaxies with similar mass.
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 halos 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 3-D (\fat) and 2-D (ROTCUR) tilted ring fitting routines, into mass densities. We find that the average slope (\(\alpha = -1.39 \pm 0.19\)), obtained from 3-D fitting is consistent with that expected from an NFW profile. On the other hand, the average slope measured using the 2-D 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.
Angular momentum of dwarf galaxies Kurapati, Sushma; Chengalur, Jayaram N; Pustilnik, Simon ...
arXiv.org,
05/2018
Paper, Journal Article
Odprti dostop
Mass and specific angular momentum are two fundamental physical parameters of galaxies. We present measurements of the baryonic mass and specific angular momentum of 11 void dwarf galaxies derived ...from neutral hydrogen (H{\sc i}) synthesis data. Rotation curves were measured using 3D and 2D tilted ring fitting routines, and the derived curves generally overlap within the error bars, except in the central regions where, as expected, the 3D routines give steeper curves. The specific angular momentum of void dwarfs is found to be high compared to an extrapolation of the trends seen for higher mass bulge-less spirals, but comparable to that of other dwarf irregular galaxies that lie outside of voids. As such, our data show no evidence for a dependence of the specific angular momentum on the large scale environment. Combining our data with the data from the literature, we find a baryonic threshold of \(\sim 10^{9.1}~M_{\odot}\) for this increase in specific angular momentum. Interestingly, this threshold is very similar to the mass threshold below which the galaxy discs start to become systematically thicker. This provides qualitative support to the suggestion that the thickening of the discs, as well as the increase in specific angular momentum, are both results of a common physical mechanism, such as feedback from star formation. Quantitatively, however, the amount of star formation observed in our dwarfs appears insufficient to produce the observed increase in specific angular momentum. It is hence likely that other processes, such as cold accretion of high angular momentum gas, also play a role in increasing the specific angular momentum.
We use the single-dish radio telescope FAST to map the HI in the tidally interacting NGC 4631 group with a resolution of 3.24\('\) (7 kpc), reaching a 5-\(\sigma\) column density limit of ...\(10^{17.9}\) cm\(^{-2}\) assuming a line width of 20 km s\(^{-1}\). Taking the existing interferometric HI image from the HALOGAS project of WSRT as reference, we are able to identify and characterize a significant excess of large-scale, low-density, and diffuse HI in the group. This diffuse HI extends for more than 120 kpc across, and accounts for more than one fourth of the total HI detected by FAST in and around the galaxy NGC 4631. In the region of the tidal tails, the diffuse HI has a typical column density above \(10^{19.5}\) cm\(^{-2}\), and is highly turbulent with a velocity dispersion around 50 km s\(^{-1}\). It increases in column density with the dense HI, and tends to be associated with the kinematically ``hotter'' part of the dense HI. Through simple modeling, we find that the majority of the diffuse HI in the tail region is likely to induce cooling out of the hot IGM instead of evaporating or being radiatively ionized. Given these relations of gas in different phases, the diffuse HI may represent a condensing phase of the IGM. Active tidal interactions on-going and in the past may have produced the wide-spreading HI distribution, and triggered the gas accretion to NGC 4631 through the phase of the diffuse HI.
Galaxies which hosted many core-collapse supernovae (SN) explosions can be used to study the conditions necessary for the formation of massive stars. NGC 2770 was dubbed a SN factory, because it ...hosted four core-collapse SNe in 20 years (three type Ib and one type IIn). Its star formation rate (SFR) was reported not to be enhanced and therefore not compatible with such a high SN rate. We aim at explaining the high SN rate of NGC 2770. We used archival HI line data for NGC 2770 and reinterpret the Halpha and optical continuum data. Even though the continuum-based SFR indicators do not yield high values, the dust-corrected Halpha luminosity implies a high SFR, consistent with the high SN rate. Such disparity between the SFR estimators is an indication of recently enhanced star formation activity, because the continuum indicators trace long timescale of the order of 100 Myr, unlike the line indicators, which trace timescales of the order of 10 Myr. Hence, the unique feature of NGC 2770 compared to other galaxies is the fact that it is observed very recently after the enhancement of the SFR. It also has high dust extinction, E(B-V) above 1 mag. We provide support for the hypothesis that the increased SFR in NGC 2770 is due to the interaction with its companion galaxies. We report an HI bridge between NGC 2770 and its closest companion and the existence of a total of four companions within 100 kpc (one identified for the first time). There are no clear HI concentrations close to the positions of SNe in NGC 2770 such as those detected for hosts of gamma-ray bursts (GRBs) and broad-lined SNe type Ic (IcBL). This suggests that the progenitors of type Ib SNe are not born out of recently accreted atomic gas, as was suggested for GRB and IcBL SN progenitors.
We examine the HI gas kinematics of galaxy pairs in two clusters and a group using Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pilot survey observations. We compare the HI properties ...of galaxy pair candidates in the Hydra I and Norma clusters, and the NGC 4636 group, with those of non-paired control galaxies selected in the same fields. We perform HI profile decomposition of the sample galaxies using a tool, {\sc baygaud} which allows us to de-blend a line-of-sight velocity profile with an optimal number of Gaussian components. We construct HI super-profiles of the sample galaxies via stacking of their line profiles after aligning the central velocities. We fit a double Gaussian model to the super-profiles and classify them as kinematically narrow and broad components with respect to their velocity dispersions. Additionally, we investigate the gravitational instability of HI gas disks of the sample galaxies using Toomre Q parameters and HI morphological disturbances. We investigate the effect of the cluster environment on the HI properties of galaxy pairs by dividing the cluster environment into three subcluster regions (i.e., outskirts, infalling and central regions). We find that the denser cluster environment (i.e., infalling and central regions) is likely to impact the HI gas properties of galaxies in a way of decreasing the amplitude of the kinematically narrow HI gas (\(M_{\rm{narrow}}^{\rm{HI}}\)/\(M_{\rm{total}}^{\rm{HI}}\)), and increasing the Toomre Q values of the infalling and central galaxies. This tendency is likely to be more enhanced for galaxy pairs in the cluster environment.
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