We present a spectroscopic analysis of the central disc regions of barred spiral galaxies, concentrating on the region that is swept by the bar but not including the bar itself (the `Star Formation Desert' or SFD region). New spectroscopy is presented for 34 galaxies, and the full sample analysed comprises 48 SBa - SBcd galaxies. These data confirm the full suppression of star formation within the SFD regions of all but the latest type (SBcd) galaxies. However, diffuse [NII] and H alpha line emission is detected in all galaxies. The ubiquity and homogeneous properties of this emission from SBa - SBc galaxies favour post-Asymptotic Giant Branch (p-AGB) stars as the source of this line excitation, rather than extreme Blue Horizontal Branch stars. The emission-line ratios strongly exclude any contribution from recent star formation, but are fully consistent with recent population synthesis modelling of p-AGB emission by other authors, and favour excitation dominated by ambient gas of approximately solar abundance, rather than ejecta from the AGB stars themselves. The line equivalent widths are also larger than those observed in many fully passive (e.g. elliptical) galaxies, which may also be a consequence of a greater ambient gas density in the SFD regions.
We present an analysis of the optical line emission from nearby barred galaxies, and in particular look at the radial range occupied by the bar. In many cases this region is marked by what we term a 'star formation desert', with a marked deficit of HII regions in optical narrow-band H-alpha imaging. Here we present long-slit spectroscopy revealing that such regions do have line emission, but that it is low-level, spatially smooth and almost ubiquitous. The relative strengths of the H-alpha and the spectrally adjacent [NII] lines in the regions are completely discrepant from those associated wi…
We present a study of the excitation conditions and metallicity of ionized gas (Z_gas) in eight nearby barred and unbarred spiral galaxies from the VIRUS-P Exploration of Nearby Galaxies (VENGA) survey, which provides high spatial sampling and resolution (median ~ 387 pc), large coverage from the bulge to outer disc, broad wavelength range (3600-6800 Ang.), and medium spectral resolution (~ 120 km s^-1 at 5000 Ang.). Our results are: (1) We present high resolution gas excitation maps to differentiate between regions with excitation typical of Seyfert, LINER, or recent star formation. We find L…
In many barred galaxies, star formation efficiency (SFE) in the bar is lower than those in the arm and bar-end, and its cause has still not been clear. Focusing on the strongly barred galaxy NGC 1300, we investigate the possibility that the presence of a large amount of diffuse molecular gas, which would not contribute to the SF, makes the SFE low in appearance. We examine the relation between the SFE and the diffuse molecular gas fraction ($f_{\rm dif}$), which is derived using the $^{12}$CO($1-0$) flux obtained from the interferometer of ALMA 12-m array, which has no sensitivity on diffuse (…
We investigate three barred lenticular galaxies (NGC 2681, NGC 3945 and NGC 4371) which were previously reported to have complex central structures but without a detailed structural analysis of these galaxies' high-resolution data. We have therefore performed four- to six-component (pseudo-)bulge/disk/bar/ring/point source) decompositions of the composite (Hubble Space Telescope plus ground-based) surface brightness profiles. We find that NGC 2681 hosts three bars, while NGC 3945 and NGC 4371 are double- and single-barred galaxies, respectively, in agreement with past isophotal analysis. We fi…
We conduct spectral line survey observations in the 3 mm band toward a spiral arm, a bar-end, and a nuclear region of the nearby barred spiral galaxy NGC 3627 with the IRAM 30 m telescope and the Nobeyama 45 m telescope. Additional observations are performed toward the spiral arm and the bar-end in the 2 mm band. We detect 8, 11, and 9 molecular species in the spiral arm, the bar-end, and the nuclear region, respectively. Star-formation activities are different among the three regions, and in particular, the nucleus of NGC 3627 is known as a LINER/Seyfert 2 type nucleus. In spite of these phys…
NGC 5850 is a nearby (z=0.0085) early type spiral galaxy classified as LINER. It is considered as a prototype double-barred system. Our optical Integral Field Spectroscopic (IFS) data of the central 21x19 arcsec^2 of NGC 5850 show extended LINER-like emission which we ascribe to the presence of a hot and evolved stellar population, possibly together with a faint AGN. Additionally NGC 5850 shows extended `composite' ionization patterns, likely to stem from a mixture of LINER-like ionization and photoionization by star formation. The kinematics of the gas deviates strongly from a simple rotation…
We present a near-infrared (NIR) imaging study of barred low surface brightness (LSB) galaxies using the TIFR near-infrared Spectrometer and Imager (TIRSPEC). LSB galaxies are dark matter dominated, late type spirals that have low luminosity stellar disks but large neutral hydrogen (HI) gas disks. Using SDSS images of a very large sample of LSB galaxies derived from the literature, we found that the barred fraction is only 8.3%. We imaged twenty five barred LSB galaxies in the J, H, K$_S$ wavebands and twenty nine in the K$_S$ band. Most of the bars are much brighter than their stellar disks, …
Machine learning technique for morphological classification of galaxies from SDSS. IV. Visual inspection vs CNN for merging, irregular, edge-on, barred, ringed, and with dust lanes galaxies at 0.02<z<0.1
Main Astronomical Observatory of the NAS of Ukraine（乌克兰国家科学院主天文台）
Cloud-cloud collision (CCC) has been suggested as a mechanism to induce massive star formation. Recent simulations suggest that a CCC speed is different among galactic-scale environments, which is responsible for observed differences in star formation activity. In particular, a high-speed CCC is proposed as a cause of star formation suppression in the bar regions in barred spiral galaxies. Focusing on the strongly barred galaxy NGC1300, we investigate the CCC speed. We find the CCC speed in the bar and bar-end tend to be higher than that in the arm. The estimated CCC speed is $\sim20~\rm km~s^…
We present millimeter molecular-line complemented by optical observations, along with a reanalysis of archival centimeter HI and continuum data, to infer the global dynamics and determine where dense molecular gas and massive stars preferentially form in the circumnuclear starburst ring of the barred-spiral galaxy NGC 7552. We find diffuse molecular gas in a pair of dust lanes each running along the large-scale galactic bar, as well as in the circumnuclear starburst ring. We do not detect dense molecular gas in the dust lanes, but find such gas concentrated in two knots where the dust lanes ma…
We present spatially resolved emission diagnostics for eight $z\sim0.9$ galaxies that demonstrate extended low ionization emission-line regions (LIERs) over kpc scales. Eight candidates are selected based on their spatial extent and emission line fluxes from slitless spectroscopic observations with the HST/WFC3 G141 and G800L grisms in the well-studied GOODS survey fields. Five of the candidates (62.5%) are matched to X-ray counterparts in the \textit{Chandra X-Ray Observatory} Deep Fields. We modify the traditional Baldwin-Philips-Terlevich (BPT) emission line diagnostic diagram to use [SII]/…
In this paper we study the nuclear obscuration of galaxies hosting LINERs based on their X-ray and optical emission. They show column densities (N_H) at soft energies (0.5-2 keV) mostly related to the diffuse emission around the AGN, showing a correlation with the optical extinction. N_H at hard energies (2-10 keV) seem to be much higher than what would be expected from the optical extinction. They might be associated to the inner regions of the AGN, buried at optical wavelengths. The main result of this paper is that around 50% of our LINER sample shows signatures of Compton-thickness (CT) ac…
CO(2-1) emission is often used as a tracer of the giant molecular clouds (GMCs) as an alternative to CO(1-0) emission in recent years. Therefore, understanding the environmental dependence of the line ratio of CO(2-1)/CO(1-0), $R_{21}$, on GMC scale is important to accurately estimate the mass of the GMCs. We thus measured the $R_{21}$ in the strongly barred galaxy NGC1300, where star formation activity strongly depends on galactic structure, on $\sim 100$ pc scale. CO images were obtained from ALMA and Nobeyama 45-m telescope. The resultant typical $R_{21}$ in NGC1300 is $0.57 \pm 0.06$. We f…
Tracing evolutionary pathways of bar-driven quenching in local Universe disc galaxies
Indian Institute of Astrophysics（印度天文物理研究所）；Pondicherry University（本地治里大学）；Leibniz-Institut für Astrophysik Potsdam（波茨坦莱布尼茨天文物理研究所）；Ludwig-Maximilians-Universitat（路德维希-马克西米利安大学）
We present the results of the wide-field $^{12}$CO (1--0) observations of the nearby barred galaxy M83 carried out with the Nobeyama Millimeter Array (NMA). The interferometric data are combined with the data obtained with the Nobeyama 45-m telescope to recover the total-flux. The target fields of the observations cover the molecular bar and part of the spiral arms, with a spatial resolution of ~110 pc x 260 pc. By exploiting the resolution and sensitivity to extended CO emission, the impact of the galactic structures on the molecular gas content is investigated in terms of the gas kinematics …
Context: Dust in late-type galaxies in the local Universe is responsible for absorbing approximately one third of the energy emitted by stars. It is often assumed that dust heating is mainly attributable to the absorption of UV and optical photons emitted by the youngest (<= 100 Myr) stars. Consequently, thermal re-emission by dust at FIR wavelengths is often linked to the star-formation activity of a galaxy. However, several studies argue that the contribution to dust heating by much older stars might be more significant. Advances in radiation transfer (RT) simulations finally allow us to act…
We present high spatial resolution, integral field spectrograph (IFS) observations of the nearby LINER (low ionization nuclear emission line region) galaxy NGC 404 at 1.25 $μ$m (J band) and 2.2 $μ$m (K band) near-infrared wavelengths. Although NGC 404 is thought to host an intermediate mass black hole at its center, it has been unclear whether accretion onto the black hole or another mechanism such as shock excitation drives its LINER emission at optical/near-infrared wavelengths. We use the OSIRIS IFS at Keck Observatory behind laser guide star adaptive optics to map the strength and kinemati…
The phenomenological study of evolving galaxy populations has shown that star forming galaxies can be quenched by two distinct processes: mass quenching and environment quenching (Peng et al. 2010). To explore the mass quenching process in local galaxies, we study the massive central disk galaxies with stellar mass above the Schechter characteristic mass. In Zhang et al. (2019), we showed that during the quenching of the massive central disk galaxies as their star formation rate (SFR) decreases, their molecular gas mass and star formation efficiency drop rapidly, but their HI gas mass remains …
MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a SDSS-IV survey that will obtain spatially resolved spectroscopy from 3600 Å to 10300 Å for a representative sample of over 10000 nearby galaxies. In this paper we present the analysis of nebular emission line properties in 14 galaxies obtained with P-MaNGA, a prototype of the MaNGA instrument. Using spatially resolved diagnostic diagrams we find extended star formation in galaxies that are centrally dominated by Seyfert/LINER-like emission, which illustrates that galaxy characterisations based on single fibre spectra are necessar…
Orbit-based structural decomposition and stellar population recovery for edge-on barred galaxies
Westlake University（西湖大学）；Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；Villanova University（维拉诺瓦大学）；University of Michigan（密歇根大学）；University of Vienna（维也纳大学）；Cardiff University（卡迪夫大学）
The diffuse ionized gas (DIG) is an important component of the interstellar medium that can provide insights into the different physical processes affecting the gas in galaxies. We utilise optical IFU observations of 71 gas-stripped and control galaxies from the Gas Stripping Phenomena in galaxies (GASP) survey, to analyze the gas properties of the dense ionized gas and the DIG, such as metallicity, ionization parameter log(q), and the difference between the measured $\log[OI]/Hα$ and the value predicted by star-forming models, given the measured log[OIII]/H$β$ ($Δlog[OI]/Hα$). We compare thes…
High Resolution (<100pc) Ionization Structures in the ISM of AGN ESO~137-G34
Astronomical Observatory of the Jagiellonian University（雅盖隆大学天文台）；NASA-Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；Newcastle University（纽卡斯尔大学）；Max Planck Institute for Extraterrestrial Physics（马克斯·普朗克地外物理学研究所）
We present results from the first public data release of the MaNGA-ARO Survey of CO Targets (MASCOT), focussing our study on galaxies whose star-formation rates and stellar masses place them below the ridge of the star-forming Main Sequence. In optically-selected type 2 AGN/LINERs/Composites, we find an empirical relation between gas-phase metallicity gradients $\nabla Z$ and global molecular gas depletion times $t_\mathrm{dep} = M_{H_2}$/SFR with "more quenched" systems showing flatter/positive gradients. Our results are based on the O3N2 metallicity diagnostic (applied to star-forming region…
DIGging into HII regions: the role of ionizing photon leakage and spectral hardening in coupling HII regions and diffuse ionized gas
Kavli Institute for Particle Astrophysics & Cosmology, Stanford University（斯坦福大学卡弗里粒子天体物理与宇宙学研究所）；Center for Decoding the Universe, Stanford University（斯坦福大学解码宇宙中心）；Racah Institute of Physics, The Hebrew University of Jerusalem（耶路撒冷希伯来大学拉卡物理学研究所）；Universität Heidelberg, Zentrum für Astronomie, Astronomisches Rechen-Institut（海德堡大学天文中心计算天文研究所）；Observatories of the Carnegie Institution for Science（卡内基科学学会天文台）；Department of Astronomy & Astrophysics, University of California, San Diego（加州大学圣地亚哥分校天文学与天体物理学系）；Department of Astronomy and Joint Space-Science Institute, University of Maryland, College Park（马里兰大学学院公园分校天文学系与联合空间科学研究所）；Departamento de Astronomía, Universidad de Chile（智利大学天文学系）；Max-Planck-Instit（马克斯·普朗克研究所）
The Star Formation Rate (SFR) was determined from a sample of 36 late-type galaxies (14 dS and 22 Sm), from the H(alpha) and Far Ultraviolet (FUV) flux. We found that the SFR(FUV) was in most cases higher than the SFR(H(alpha)).We also obtained that the SFR is larger for Sm galaxies and smaller for barred galaxies, for any morphological type, in both diagnostic methods. In addition, a study of the spatial distribution of star formation within these galaxies was made, concluding that there is not a preferential place for the star formation. Finally, we studied the role of the Diffuse Ionized Ga…
Based on MUSE data from the GASP survey, we study the Halpha-emitting extraplanar tails of 16 cluster galaxies at z~0.05 undergoing ram pressure stripping. We demonstrate that the dominating ionization mechanism of this gas (between 64% and 94% of the Halpha emission in the tails depending on the diagnostic diagram used) is photoionization by young massive stars due to ongoing star formation (SF) taking place in the stripped tails. This SF occurs in dynamically quite cold HII clumps with a median Halpha velocity dispersion sigma = 27 km s^-1. We study the characteristics of over 500 star-formi…
Our Galaxy, the Milky Way, is a benchmark for understanding disk galaxies. It is the only galaxy whose formation history can be studied using the full distribution of stars from white dwarfs to supergiants. The oldest components provide us with unique insight into how galaxies form and evolve over billions of years. The Galaxy is a luminous (L-star) barred spiral with a central box/peanut bulge, a dominant disk, and a diffuse stellar halo. Based on global properties, it falls in the sparsely populated "green valley" region of the galaxy colour-magnitude diagram. Here we review the key integrat…
Within the NUclei of GAlaxies project we have obtained IRAM PdBI and 30m 12CO(1-0) and 12CO(2-1) observations of the spiral galaxy NGC 6951. Previous work shows that there is indirect evidence of gas inflow from 3 kpc down to small radii: a large-scale stellar bar, a prominent starburst ring (r~580 pc) and a LINER/Seyfert 2 nucleus. In this paper we study the gas kinematics as traced by the CO line emission in detail. We quantify the influence of the large-scale stellar bar by constructing an analytical model of the evolution of gas particles in a barred potential. From this model gravitationa…
We present interferometric observations of CO lines (12CO(1-0, 2-1) and 13CO(1-0, 2-1)) and dense gas tracers (HCN(1-0), HCO+(1-0), HNC(1-0) and HNCO(4-3)) in two nearby edge-on barred lenticular galaxies, NGC 4710 and NGC 5866, with most of the gas concentrated in a nuclear disc and an inner ring in each galaxy. We probe the physical conditions of a two-component molecular interstellar medium in each galaxy and each kinematic component by using molecular line ratio diagnostics in three complementary ways. First, we measure the ratios of the position-velocity diagrams of different lines, secon…
Radio synchrotron emission is a powerful tool to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 μG) and in central starburst regions (50-100 μG). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. -- Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fi…
Early Results from the Coma Legacy IFU Survey (CLIFS): Ram Pressure Induced Shocks and Ionization in Jellyfish Tails
McMaster University（麦克马斯特大学）；University of Waterloo（滑铁卢大学）；Cardiff University（卡迪夫大学）；Astronomical Observatory of Padova（帕多瓦天文台）；University of Birmingham（伯明翰大学）；University of Cape Town（开普敦大学）
In this paper, we investigate 2727 galaxies observed by MaNGA as of June 2016 to develop spatially resolved techniques for identifying signatures of active galactic nuclei (AGN). We identify 303 AGN candidates. The additional spatial dimension imposes challenges in identifying AGN due to contamination from diffuse ionized gas, extra-planar gas and photoionization by hot stars. We show that the combination of spatially-resolved line diagnostic diagrams and additional cuts on H$α$ surface brighness and H$α$ equivalent width can distinguish between AGN-like signatures and high-metallicity galaxie…
We reveal the importance of ongoing in-situ star formation in the Brightest Cluster Galaxy in the massive cool-core CLASH cluster MACS 1931.8-2635 at z=0.35. Using a multi-wavelength approach, we assess the stellar and warm ionized medium components, spatially resolved by the VLT-MUSE spectroscopy, and link them to the molecular gas by incorporating sub-mm ALMA observations. We measure the fluxes of strong emission lines, allowing us to determine the physical conditions of the warm ionized gas. The ionized gas flux brightness peak corresponds to the location of the supermassive black hole and …
