We present a Far-Ultraviolet (FUV) study of sixteen star-forming dwarf galaxies (SFDGs) using the Ultraviolet Imaging Telescope (UVIT). Morphologically, SFDGs are classified as dwarf spirals, dwarf irregulars, and blue compact dwarfs (BCDs). We extracted the star-forming complexes (SFCs) from the sample galaxies, derived their sizes, and estimated the FUV+24$μm$ star formation rates (SFRs). We also determined the approximate stellar disk mass associated with the SFCs using IRAC 3.6-micron images. We derived the specific SFRs (sSFRs), as well as the SFR densities ($Σ(SFR)$) for the SFCs. We find that the lower $Σ(SFR)$ for each type is different, with the dwarf irregulars having the lowest $Σ(SFR)$ compared to others. However, the median size of the SFCs in the dwarf irregulars is the largest compared to the other two types when compared at roughly the same distance. We have derived the star-forming main sequence (SFMS) on the scale of SFCs for all three classes of SFDGs. We find that although all SFDGs approximately follow the global SFMS relation, i.e. $SFR\propto {M_{*}}^α$ (where globally $α\approx1$ for low surface brightness galaxies and $0.9$ for SFDGs), on the scale of SFCs the $α$ value for each type is different. The $α$ values for dwarf spirals, dwarf irregulars, and BCDs are found to be 0.74$\pm$0.13, 0.8$\pm$0.16, and 0.8$\pm$0.19, respectively. However, the age of all SFCs approximately corresponds to 1 Gyr. Finally, we find that the outer SFCs in most galaxies except BCDs have a high sSFR, supporting the inside-out model of galaxy growth.
Secular and environmental effects play a significant role in regulating the star formation rate and hence the evolution of the galaxies. Since UV flux is a direct tracer of the star formation in galaxies, the UltraViolet Imaging Telescope (UVIT) onboard ASTROSAT enables us to characterize the star forming regions in a galaxy with its remarkable spatial resolution. In this study, we focus on the secular evolution of NGC 628, a spiral galaxy in the local universe. We exploit the resolution of UVIT to resolve up to $\sim$ 63 pc in NGC 628 for identification and characterization of the star formin…
We report the discovery of a nearby large, diffuse galaxy that shows star formation, using Ultra Violet Imaging Telescope (UVIT) far-UV observations, archival optical data from Multi-Unit Spectroscopic Explorer (MUSE) and Dark Energy Camera Legacy Survey (DECaLS), and InfraRed Survey Facility (IRSF) near-infrared observations. The galaxy was not detected earlier due to its superposition with the background galaxy, NGC 6902A. They were together mistakenly classified as an interacting system. NGC 6902A is at a redshift of 0.05554, but MUSE observations indicate that the interacting tail is a sep…
Star formation in galaxies is a hierarchical process with a wide range of scales from smaller clusters to larger stellar complexes. Here, we present an ultra-violet imaging study of the nearby flocculent spiral galaxy NGC 7793, observed with the Ultra-Violet Imaging Telescope (UVIT). We find that the disk scale-length estimated in Far-UV (2.64$\pm$0.16 kpc) is larger than that in Near-UV (2.21$\pm$0.21 kpc) and optical (1.08 kpc), which supports the inside-out growth scenario of the galaxy disk. The star-forming UV disk is also found to be contained within the extent of H~I gas of column densi…
We present a study of star forming regions and its demographics in the nearby dwarf irregular galaxy WLM using the Ultra-Violet Imaging Telescope (UVIT) multi band observations in three filters F148W, N245M and N263M. We find that the UV emission is extended at least up to 1.7 kpc, with the NUV emission more extended than the FUV. We create UV color maps ((F148W$-$N245M) and (F148W$-$N263M)) to study the temperature morphology of young stellar complexes with the help of theoretical models. We identify several complexes with temperature T $>$ 17500 K which are likely to be the OB associations p…
We present a far-UV (FUV) and near-UV (NUV) imaging study of recent star formation in the nearby spiral galaxy NGC 2336 using the Ultraviolet Imaging Telescope (UVIT). NGC 2336 is nearly face-on in morphology and has a multi-armed, branching spiral structure which is associated with star forming regions distributed mainly along the spiral arms and the co-rotation ring around the bar. We have identified 72 star forming knots in the disk, of which only two are in the inter-arm regions and 6 in the co-rotation ring. We have tabulated their positions and estimated their luminosities, sizes, star f…
We present a far-UV (FUV) study of the star-forming complexes (SFCs) in three nearby galaxies using the Ultraviolet Imaging Telescope (UVIT). The galaxies are close to face-on and show significant outer disk star formation. Two of them are isolated (NGC 628, NGC 6946), and one is interacting with distant companions (NGC 5457). We compared the properties of the SFCs inside and outside the optical radius (R$_{25}$). We estimated the sizes, star formation rates (SFRs), metallicities, and the Toomre Q parameter of the SFCs. We find that the outer disk SFCs are at least ten times smaller in area th…
AstroSat-UVIT observations of a possibly interacting pair of galaxies in HCG 77
Indian Institute of Science Education and Research, Mohali（印度科学教育研究所穆哈利分校）；Thapar Institute of Engineering and Technology, Patiala（塔帕尔工程技术学院帕蒂亚拉分校）；Tata Institute of Fundamental Research, Mumbai（塔塔基础研究所孟买分校）
We present an ultra-violet study of two nearby dwarf irregular galaxies WLM and IC~2574, using the Far-UV and Near-UV data from the Ultra-Violet Imaging Telescope (UVIT). We used the F148W band Far-UV images and identified 180 and 782 young star-forming clumps in WLM and IC~2574, respectively. The identified clumps have sizes between 7 - 30 pc in WLM and 26 - 150 pc in IC~2574. We noticed more prominent hierarchical splitting in the structure of star-forming regions at different flux levels in IC~2574 than WLM. We found that the majority of the clumps have elongated shapes in the sky plane wit…
$\require{mediawiki-texvc}$ Supermassive black holes at the centre of active galactic nuclei (AGN) produce relativistic jets that can affect the star formation characteristics of the AGN hosts. Observations in the ultraviolet (UV) band can provide an excellent view of the effect of AGN jets on star formation. Here, we present a census of star formation properties in the Northern Star-forming Region (NSR) that spans about 20 kpc of the large radio source Centaurus A hosted by the giant elliptical galaxy NGC 5128. In this region, we identified 352 UV sources associated with Cen A using new obser…
Investigating the young stellar populations and hierarchies in nearby galaxies with the UVIT. II. Presenting the properties of ~25,000 UV-detected star-forming clumps
Indian Institute of Astrophysics（印度天体物理研究所）；Pondicherry University（本地治里大学）；Leibniz-Institut für Astrophysik Potsdam（波茨坦阿诺德·爱因斯坦 Leibniz 天体物理研究所）；S. N. Bose National Centre for Basic Sciences（S.N. 玻色基础科学国立中心）；Academia Sinica Institute of Astronomy and Astrophysics (ASIAA)（中央研究院天文及天文物理研究所）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理学中心）；Department of Physics and Astronomy, Rutgers University（罗格斯大学物理与天文学系）
Star forming dwarf galaxies in the local volume are diverse and are ideal test beds to understand details of star formation in a variety of environments. Here, we present a deep FUV imaging study of a nearby dwarf irregular galaxy IC 2574 using the Ultraviolet Imaging Telescope (UVIT). We identified 419 FUV bright regions with radii between 15 - 285 pc in the galaxy and found that 28.6\% of them to be located in H~I shells, 12.6\% inside holes and 60.1\% to be away from the holes. The H~I column density is found to be more than $10^{21} cm^{-2}$ for 82.3\% of the identified regions. 30 out of …
We present analysis of the far ultraviolet (FUV) emission of sources in the central region of the Coma cluster (z=0.023) using the data taken by the UVIT aboard the multi-wavelength satellite mission AstroSat. We find a good correlation between the UVIT FUV flux and the fluxes in both wavebands of the Galex mission, for the common sources. We detect stars and galaxies, amongst which the brightest (r <= 17 mag) galaxies in the field of view are mostly members of the Coma cluster. We also detect three quasars (z = 0.38, 0.51, 2.31), one of which is likely the farthest object observed by the UVIT…
A FUV-optical approach for studying hierarchical star formation in nearby galaxies with UVIT
Indian Institute of Astrophysics（印度天体物理研究所）；Pondicherry University（本地治里大学）；Leibniz-Institut fur Astrophysik Potsdam (AIP)（波茨坦阿基米德天体物理研究所）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理学中心）；Rutgers University（罗格斯大学）；S. N. Bose National Centre for Basic Sciences（S.N.玻色基础科学国家中心）；Academia Sinica Institute of Astronomy and Astrophysics (ASIAA)（中央研究院天文及天文物理研究所）
Some post-merger galaxies are known to undergo a starburst phase that quickly depletes the gas reservoir and turns it into a red-sequence galaxy, though the details are still unclear. Here we explore the pattern of recent star formation in the central region of the post-merger galaxy NGC7252 using high resolution UV images from the UVIT on ASTROSAT. The UVIT images with 1.2 and 1.4 arcsec resolution in the FUV and NUV are used to construct a FUV-NUV colour map of the central region. The FUV-NUV pixel colour map for this canonical post-merger galaxy reveals a blue circumnuclear ring of diameter…
The spatial distribution and physical sizes of star forming clumps at the smallest scales provide valuable information on hierarchical star formation (SF). In this context, we report the sites of ongoing SF at ~120 pc along the interacting galaxies in Stephan's Quintet (SQ) compact group using AstroSat-UVIT and JWST data. Since ultraviolet radiation is a direct tracer of recent SF, we identified star forming clumps in this compact group from the FUV imaging which we used to guide us to detect star forming regions on JWST IR images. The FUV imaging reveals star forming regions within which we d…
Investigating the Young Stellar Populations and Hierarchies in Nearby Galaxies with the UVIT. III. Evidence for a Largest Scale of Correlated Stellar Structures and a Non-universal Fractal Dimension
Indian Institute of Astrophysics（印度天体物理研究所）；Pondicherry University（本地治里大学）；Leibniz-Institut für Astrophysik Potsdam（波茨坦莱布尼茨天体物理研究所）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理学中心）；Rutgers University（罗格斯大学）；S. N. Bose National Centre for Basic Sciences（S.N. 玻色基础科学国家中心）；Australian National University（澳大利亚国立大学）；Macquarie University（麦考瑞大学）；IIT (BHU)（印度技术学院（贝拿勒斯印度教大学））
We report the discovery of a bright, compact ultraviolet source at a projected separation of 1.1~kpc from the known active galactic nucleus (AGN) in Mrk~766 based on Astrosat/UVIT observations. We perform radial profile analysis and derive the UV flux almost free from the nearby contaminating sources. The new source is about 2.5 and 5.6 times fainter than the AGN in the far and near UV bands. The two sources appear as a pair of nuclei in Mrk~766. We investigate the nature of the new source based on the UV flux ratio, X-ray and optical emission. The new source is highly unlikely to be another a…
We present the far ultraviolet (FUV) imaging of the nearest Jellyfish or Fireball galaxy IC3418/VCC 1217, in the Virgo cluster of galaxies, using Ultraviolet Imaging Telescope (UVIT) onboard the ASTROSAT satellite. The young star formation observed here in the 17 kpc long turbulent wake of IC3418, due to ram pressure stripping of cold gas surrounded by hot intra-cluster medium, is a unique laboratory that is unavailable in the Milkyway. We have tried to resolve star forming clumps, seen compact to GALEX UV images, using better resolution available with the UVIT and incorporated UV-optical imag…
A pilot method to determine the high mass end of the Stellar Initial Mass Function in galaxies using UVIT, H$α$-MUSE observations and applied to NGC628
The absence of star formation in the bar region that has been reported for some galaxies can theoretically be explained by shear. However, it is not clear how star-forming (SF) bars fit into this picture and how the dynamical state of the bar is related to other properties of the host galaxy. We used integral-field spectroscopy from VLT/MUSE to investigate how star formation within bars is connected to structural properties of the bar and the host galaxy. We derived spatially resolved H$α$ fluxes from MUSE observations from the CARS survey to estimate star formation rates in the bars of 16 nea…
Star-forming regions on different scales, such as giant molecular clouds in our Galaxy and star-forming galaxies, emit GeV gamma-rays. These are thought to originate from hadronic interactions of cosmic-ray (CR) nuclei with the interstellar medium. It has recently been shown that the gamma-ray luminosity ($L_γ$) of star-forming galaxies is well correlated with their star formation rates (SFR). We investigated \textsl{Fermi} data of eight Galactic molecular clouds in the Gould belt and found that molecular clouds do not follow the $L_γ-{\rm SFR}$ correlation of star-forming galaxies. We also co…
The HII regions are all studied employing the same general prescriptions, despite the possible influence of their environment in their star formation processes. Through the analysis of two samples of 725 inner and 671 outer disk HII region observed spectra, we explore possible systematic differences between their ionising clusters physical properties (metallicity, mass, and age), comparing observations and predictions by photoionisation models. Higher metallicities are confirmed for inner regions, although there are important discrepancies between the diagnostic diagrams. Calibrations based on…
We present a UV study of 3 extended UV (XUV) galaxies that we have observed with the UVIT and the GMRT. XUV galaxies show filamentary or diffuse star formation well beyond their optical disks, in regions where the disk surface density lies below the threshold for star formation. GALEX observations found that surprisingly 30% of all the nearby spiral galaxies have XUV disks. The XUV galaxies can be broadly classified as type 1 and type 2 XUV disks. The type 1 XUV disks have star formation that is linked to that in their main disk, and the UV emission appears as extended, filamentary spiral arms…
We present a comparative study of a set of star-formation rate tracers based on mid-infrared emission in the 12.81$μ$m [Ne II] line, the 15.56$μ$m [Ne III] line, and emission features from polycyclic aromatic hydrocarbons (PAHs) between 5.2 and 14.7$μ$m. We calibrate our tracers with the thermal component of the radio continuum emission at 33 GHz from 33 extranuclear star-forming regions observed in nearby galaxies. Correlations between mid-IR emission features and thermal 33 GHz star-formation rates (SFR) show significant metallicity-dependent scatter and offsets. We find similar metallicity-…
PAH emission from star-forming and quiescent galaxies at $z=0.5-0.8$ probed by JWST/MIRI
S. N. Bose National Centre for Basic Sciences（S.N. 玻色基础科学国家中心）；Academia Sinica Institute of Astronomy and Astrophysics (ASIAA)（中央研究院天文及天文物理研究所）；East Asian Observatory（东亚天文台）；Inter-University Centre for Astronomy and Astrophysics（大学间天文学和天体物理学中心）；IPAC, California Institute of Technology（加州理工学院行星与红外天文中心）；Centro de Astrobiología (CAB), CSIC-INTA（天体生物学中心）
Interacting galaxies are known to have higher global rates of star formation on average than normal galaxies, relative to their stellar masses. Using UV and IR photometry combined with new and published H-alpha images, we have compared the star formation rates of ~700 star forming complexes in 46 nearby interacting galaxy pairs with those of regions in 39 normal spiral galaxies. The interacting galaxies have proportionally more regions with high star formation rates than the spirals. The most extreme regions in the interacting systems lie at the intersections of spiral/tidal structures, where …
We present a comparative study of CO and polycyclic aromatic hydrocarbon (PAH) emission toward a region including the massive star-forming regions of NGC 6334 and NGC 6357. We use the NANTEN $^{12}$CO($J$ = 1--0) data and the $AKARI$ 9 $μ$m All-Sky diffuse map in order to evaluate the calibration accuracy of the $AKARI$ data. We confirm that the overall CO distribution shows a good spatial correspondence with the PAH emission, and their intensities exhibit a good power-law correlation with a spatial resolution down to 4$'$ over the region of 10$^\circ$$\times$10$^\circ$. We also reveal poorer …
The PHANGS-AstroSat Atlas of Nearby Star Forming Galaxies
University of Alberta（阿尔伯塔大学）；Harvard & Smithsonian（哈佛-史密森天体物理中心）；University of Calgary（卡尔加里大学）；The Johns Hopkins University（约翰斯·霍普金斯大学）；The Ohio State University（俄亥俄州立大学）；Max Planck Institut für Astronomie（马克斯·普朗克天文研究所）；INAF — Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）；Argelander-Institut für Astronomie, Universität Bonn（波恩大学阿尔兰德天体物理研究所）；Instituto de Alta Investigación, Universidad de Tarapacá（塔拉帕卡大学高级研究院）
We present a comparative study of the relation between the aperture-based gas-phase metallicity and three structural parameters of star-forming galaxies: mass ($\mathrm{M \equiv M_*}$), average potential ($Φ\equiv \mathrm{M_*/R_e}$) and average surface mass density ($Σ\equiv \mathrm{M_*/R_e^2}$; where $\mathrm{R_e}$ is the effective radius). We use a volume-limited sample drawn from the publicly available SDSS DR7, and base our analysis on aperture-matched sampling by selecting sets of galaxies where the SDSS fibre probes a fixed fraction of $\mathrm{R_e}$. We find that between 0.5 and 1.5 $\m…
We investigate the relationship between environment and the galaxy main sequence (the relationship between stellar mass and star formation rate) and also the relationship between environment and radio luminosity (P$_{\rm 1.4GHz}$) to shed new light on the effects of the environments on galaxies. We use the VLA-COSMOS 3 GHz catalogue that consists of star-forming galaxies (SFGs) and quiescent galaxies (AGN) in three different environments (field, filament, cluster) and for three different galaxy types (satellite, central, isolated). We perform for the first time a comparative analysis of the di…
We present the KMOS-CLASH (K-CLASH) survey, a K-band Multi-Object Spectrograph (KMOS) survey of the spatially-resolved gas properties and kinematics of 191 (predominantly blue) H$α$-detected galaxies at $0.2 \lesssim z \lesssim 0.6$ in field and cluster environments. K-CLASH targets galaxies in four Cluster Lensing And Supernova survey with Hubble (CLASH) fields in the KMOS $IZ$-band, over $7'$ radius ($\approx2$-$3$ Mpc) fields-of-view. K-CLASH aims to study the transition of star-forming galaxies from turbulent, highly star-forming disc-like and peculiar systems at $z\approx1$-$3$, to the co…
The star-forming reservoir in the distant Universe can be detected through HI 21-cm absorption arising from either cool gas associated with a radio source or from within a galaxy intervening the sight-line to the continuum source. In order to test whether the nature of the absorber can be predicted from the profile shape, we have compiled and analysed all of the known redshifted (z > 0.1) HI 21-cm absorption profiles. Although between individual spectra there is too much variation to assign a typical spectral profile, we confirm that associated absorption profiles are on average, wider than th…
Aims.Molecular masers, including methanol and hydroxyl masers, and in particular the ones in excited rotational states (ex-OHmasers), are one of the most informative tools for studying star-forming regions. So, the discovery, of new maser sources in theseregions is of great importance. Many studies and surveys of ex-OH maser sources have been carried out in the southern celestialhemisphere, but only a few have been done in the northern hemisphere. The specific aim of this work is to close this gap.Methods.The star-forming regions in the northern hemisphere with known active methanol masers wer…
We examine the properties of the circumgalactic medium (CGM) at low redshift in a range of simulated Milky Way mass halos. The sample is comprised of seven idealized simulations, an adaptive mesh refinement cosmological zoom-in simulation, and two groups of 50 halos with star forming or quiescent galaxies taken from the IllustrisTNG100 simulation. The simulations have very different setups, resolution, and feedback models, but are analyzed in a uniform manner. By comparing median radial profiles and mass distributions of CGM properties, we isolate key similarities and differences. In doing so,…
