分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present a study of the size--mass relation for local post-starburst (PSB)
galaxies at $z\lesssim0.33$ selected from the Sloan Digital Sky Survey Data
Release 8. We find that PSB galaxies with stellar mass ($M_*$) at
$10^9~M_{\odot}
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We use 789 disk-like, star-forming galaxies (with 596 HI detections) from HI follow-up observations for the SDSS-IV MaNGA survey to study the possible role of inner HI gas in causing secondary dependences in the mass-gas-phase metallicity relation. We use the gas-phase metallicity derived at the effective radii of the galaxies. We derive the inner HI mass witHIn the optical radius, but also use the total HI mass and star formation rate (SFR) for a comparison. We confirm the anticorrelation between the total HI mass and gas-phase metallicity at fixed stellar mass, but the anticorrelation is significantly strengthened when the total HI mass is replaced by the inner HI mass. Introducing a secondary relation with the inner HI mass can produce a small but noticeable decrease (16%) in the scatter of the mass-gas-phase metallicity relation, in contrast to the negligible effect with the SFR. The correlation with the inner HI mass is robust when using different diagnostics of metallicity, but the correlation with SFR is not. The correlation with the inner HI mass becomes much weaker when the gas-phase metallicity is derived in the central region instead of at the effective radius. These results support the idea that the scatter in the mass-metallicity relation is regulated by gas accretion, and not directly by the SFR, and stress the importance of deriving the gas mass and the metallicity from roughly the same region. The new relation between inner HI mass and gas-phase metallicity will provide new constraints for chemical and galaxy evolution models.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： NGC 2915 is a unique nearby galaxy that is classified as an isolated blue compact dwarf based on its optical appearance but has an extremely extended H i gas disk with prominent Sd-type spiral arms. To unveil the starburst-triggering mystery of NGC 2915, we performed a comprehensive analysis of deep VLT/MUSE integral field spectroscopic observations that cover the star-forming region in the central kiloparsec of the galaxy. We find that episodes of bursty star formation have recurred in different locations throughout the central region, and the most recent one peaked around 50 Myr ago. The bursty star formation has significantly disturbed the kinematics of the ionized gas but not the neutral atomic gas, which implies that the two gas phases are largely spatially decoupled along the line of sight. No evidence for an active galactic nucleus is found based on the classical line-ratio diagnostic diagrams. The ionized gas metallicities have a positive radial gradient, which confirms the previous study based on several individual H ii regions and may be attributed to both the stellar feedback-driven outflows and metal-poor gas inflow. Evidence for metal-poor gas infall or inflow includes discoveries of high-speed collisions between gas clouds of different metallicities, localized gas metallicity drops and unusually small metallicity differences between gas and stars. The central stellar disk appears to be counter-rotating with respect to the extended H i disk, implying that the recent episodes of bursty star formation have been sustained by externally accreted gas.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The high-cadence survey of Zwicky Transient Facility (ZTF) has completely dominated the discovery of tidal disruption events (TDEs) in the past few years and resulted in the largest sample of TDEs with optical/UV light curves well-sampled around their peaks, providing us an excellent opportunity to construct a peak luminosity function (LF) of tidal disruption flares (TDFs). The new construction is necessary particularly considering that the most updated LF reported in literature has been inferred from only 13 sources from 5 different surveys. Here we present the optical and blackbody LFs calculated by 33 TDFs discovered in the ZTF-I survey. The optical LF can be described by both a power-law profile $dN/dL_g\propto L_g^{-2.3\pm0.2}$, and a Schechter-like function. The blackbody LF can be described by a power-law profile $dN/dL_{\rm bb}\propto L_{\rm bb}^{-2.2\pm0.2}$, shallower than the LF made of previous van Velzen (2018) sample. A possible low-luminosity turnover in the optical LF supports an Eddington-limited emission scenario. The drop of volumetric rate at high luminosity suggests a rate suppression due to direct captures of the black hole. The total volumetric rate is one order of magnitude lower than the previous estimation, which is probably not simply caused by the high fraction post-peak sources (7/13) in the previous sample. Instead, the normalization step during the previous LF construction to reconcile various surveys might adversely amplify the influence of serendipitous discoveries. Therefore, TDFs selected from ongoing and upcoming uniform surveys like ZTF, Vera Rubin Observatory (VRO) and Wide-Field Survey Telescope (WFST) should yield more accurate LFs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Optical time-domain survey has been the dominant means of hunting for rare tidal disruption events (TDEs) in the past decade and remarkably advanced the TDE study. Particularly, the Zwicky Transient Facility (ZTF) has opened the era of population studies and the upcoming Large Synoptic Survey Telescope (LSST) at the Vera Rubin Observatory (VRO) is believed to further revolutionize the field soon. Here we present the prospects of finding TDEs with another powerful survey to be performed by 2.5-metre Wide-Field Survey Telescope (WFST). The WFST, located in western China, will be the most advanced facility dedicated to optical time-domain surveys in the northern hemisphere once commissioning. We choose to assess its TDE detectability on the basis of mock observations, which is hitherto closest to reality by taking into consideration of site conditions, telescope parameters, survey strategy and transient searching pipeline. Our mock observations on 440 deg$^2$ field (CosmoDC2 catalogue) show that $29\pm6$ TDEs can be robustly found per year if observed at $u, g, r, i$ bands with 30-second exposure every 10 days, in which a discovery is defined as $\geq$10 epochal detections in at least two filters. If the WFST survey is fully optimized for discovering TDE, we would expect to identify $392\pm74$ of TDEs every year, with the redshift up to $z\sim0.8$, which poses a huge challenge to follow-up resources.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： NGC 2915 is a unique nearby galaxy that is classified as an isolated blue compact dwarf based on its optical appearance but has an extremely extended H i gas disk with prominent Sd-type spiral arms. To unveil the starburst-triggering mystery of NGC 2915, we performed a comprehensive analysis of deep VLT/MUSE integral field spectroscopic observations that cover the star-forming region in the central kiloparsec of the galaxy. We find that episodes of bursty star formation have recurred in different locations throughout the central region, and the most recent one peaked around 50 Myr ago. The bursty star formation has significantly disturbed the kinematics of the ionized gas but not the neutral atomic gas, which implies that the two gas phases are largely spatially decoupled along the line of sight. No evidence for an active galactic nucleus is found based on the classical line-ratio diagnostic diagrams. The ionized gas metallicities have a positive radial gradient, which confirms the previous study based on several individual H ii regions and may be attributed to both the stellar feedback-driven outflows and metal-poor gas inflow. Evidence for metal-poor gas infall or inflow includes discoveries of high-speed collisions between gas clouds of different metallicities, localized gas metallicity drops and unusually small metallicity differences between gas and stars. The central stellar disk appears to be counter-rotating with respect to the extended H i disk, implying that the recent episodes of bursty star formation have been sustained by externally accreted gas.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： High-resolution observations of ionized and molecular gas in the nuclear regions of galaxies are indispensable for delineating the interplay of star formation, gaseous inflows, stellar radiation, and feedback processes. Combining our new ALMA band 3 mapping and archival VLT/MUSE data, we present a spatially resolved analysis of molecular and ionized gas in the central 5.4 Kpc region of NGC 1365. We find the star formation rate/efficiency (SFR/SFE) in the inner circumnuclear ring is about 0.4/1.1 dex higher than in the outer regions. At a linear resolution of 180 pc, we obtain a super-linear Kennicutt-Schmidt law, demonstrating a steeper slope (1.96$\pm$0.14) than previous results presumably based on lower-resolution observations. Compared to the northeastern counterpart, the southwestern dust lane shows lower SFE, but denser molecular gas, and larger virial parameters. This is consistent with an interpretation of negative feedback from AGN and/or starburst, in the sense that the radiation/winds can heat and interact with the molecular gas even in relatively dense regions. After subtracting the circular motion component of the molecular gas and the stellar rotation, we detect two prominent non-circular motion components of molecular and ionized hydrogen gas, reaching a line-of-sight velocity of up to 100 km/s. We conclude that the winds or shocked gas from the central AGN may expel the low-density molecular gas and diffuse ionized gas on the surface of the rotating disk.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yao Yao
Haiyang Liu
Xu Kong
Yulong Gao
Guangwen Chen
Xinkai Chen
Zhixiong Liang
Zesen Lin
Yimeng Tang
Hongxin Zhang
摘要： The scaling relationship is a fundamental probe of the evolution of galaxies. Using the integral field spectroscopic data from the Mapping Nearby Galaxies at Apache Point Observatory survey, we select 1698 spaxels with significant detection of the auroral emission line \oiii$\lambda$4363 from 52 galaxies to investigate the scaling relationships at the low-metallicity end. We find that our sample's star formation rate is higher and its metallicity is lower in the scaling relationship than the star-forming sequence after removing the contribution of the Fundamental Metallicity Relation.We also find that the stellar ages of our sample are younger ($<$ 1 Gyr) and the stellar metallicities are also lower. Morphological parameters from Deep Learning catalog indicate that our galaxies are more likely to be merger. These results suggest that their low metallicity regions may be related to interaction, the inflow of metal-poor gas may dilute the interstellar medium and form new metal-poor stars in these galaxies during interaction.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We study the role of atomic hydrogen (HI) in regulating size growth of local galaxies. The size of a galaxy, $D_{\rm r,~25}$, is characterized by the diameter at which the $r-$band surface brightness reaches $\mu_{\rm r}=25.0~\rm mag~arcsec^{-2}$. We find that the positions of galaxies in the size ($D_{\rm r,~25}$)$-$stellar mass ($M_{\ast}$) plane strongly depend on their HI-to-stellar mass ratio ($M_{\rm HI}/M_{\ast}$). In the HI-rich regime, galaxies that are more rich in HI tend to have larger sizes. Such a trend is not seen in the HI-poor regime, suggesting that size growth is barely affected by the HI content when it has declined to a sufficiently low level. An investigation of the relations between size, $M_{\rm HI}/M_{\ast}$ and star formation rate (SFR) suggests that size is more intrinsically linked with $M_{\rm HI}/M_{\ast}$, rather than SFR. We further examine the HI-to-stellar disk size ratio ($D_{\rm HI}/D_{\rm r,~25}$) of galaxies and find that at log($M_{\rm HI}/M_{\ast})>-0.7$, $D_{\rm HI}/D_{\rm r,~25}$ is weakly correlated with $M_{\ast}$. These findings support a picture in which the HI-rich galaxies live in an inside-out disk growing phase regulated by gas accretion and star formation. The angular momentum of the accreted materials is probably the key parameter in shaping the size of an HI-rich galaxy.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Aims: There is a spatially resolved star-forming main sequence (rSFMS) and mass-metallicity relation (rMZR) of galaxies in local universe. We know that the global mass-metallicity relation (MZR) results from the integral of rMZR, and it will evolve with the redshift. However, the evolution of rMZR with redshift is still unclear due to the low spatial resolution and signal-to-noise ratio. There are currently too few observations beyond local universe, and only simulations can reproduce the evolution of rMZR with redshift. Methods: In this work, we select ten emission-line galaxies with an average redshift of $z\sim 0.26$ from MUSE-Wide DR1. We obtain the spatially resolved star formation rate (SFR) and metallicity from the integral field spectroscopy (IFS), as well as the stellar mass surface density from the 3D-HST photometry. We derive the rSFMS and rMZR at $z\sim 0.26$ and compare them with local galaxies. Results: We find the rSFMS of galaxies at $z\sim 0.26$ has a slope of $\sim$0.771. The rMZR exists at $z\sim 0.26$, showing a similar shape to the local universe but a lower average metallicity about $\sim$0.11 dex than the local one. In addition, we also study their spatially resolved fundamental metallicity relation (rFMR). However, there is no obvious evidence that rFMR exists at $z\sim$0.26 and it is not an extension of rMZR at a high SFR. Conclusions: Similar to their global versions, the rSFMS and rMZR of galaxies also evolve with redshift. Given the fixed stellar mass, galaxies at higher redshift show higher SFR and lower metallicity. These suggest that the evolution of the global galaxy properties with redshift may result from integrating the evolution of spatially resolved properties of galaxies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： To investigate the effects of environment in the quenching phase, we study
the empirical relations for green valley (GV) galaxies between overdensity and
other physical properties (i.e., effective radius $r_{\rm e}$, S\'{e}rsic
indices $n$, and specific star formation rate sSFR). Based on five 3D-{\it
HST}/CANDELS fields, we construct a large sample of 2126 massive ($M_{\star} >
10^{10} M_{\sun}$) GV galaxies at $0.5
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Several mechanisms for the transformation of blue star-forming to red quiescent galaxies have been proposed, and the green valley (GV) galaxies amid them are widely accepted in a transitional phase. Thus, comparing the morphological and environmental differences of the GV galaxies with early-type disks (ETDs; bulge dominated and having a disk) and late-type disks (LTDs; disk dominated) is suitable for distinguishing the corresponding quenching mechanisms. A large population of massive ($M_* \geqslant 10^{10}M_\odot$) GV galaxies at $0.5 \leqslant z \leqslant 1.5$ in 3D-HST/CANDELS is selected using extinction-corrected $(U-V)_{\rm rest}$ color. After eliminating any possible active galactic nucleus candidates and considering the "mass-matching", we finally construct two comparable samples of GV galaxies with either 319 ETD or 319 LTD galaxies. Compared to the LTD galaxies, it is found that the ETD galaxies possess higher concentration index and lower specific star formation rate, whereas the environments surrounding them are not different. This may suggest that the morphological quenching may dominate the star formation activity of massive GV galaxies rather than the environmental quenching. To quantify the correlation between the galaxy morphology and the star formation activity, we define a dimensionless morphology quenching efficiency $Q_{\rm mor}$ and find that $Q_{\rm mor}$ is not sensitive to the stellar mass and redshift. When the difference between the average star formation rate of ETD and LTD galaxies is about 0.7 $M_\odot \rm \;yr^{-1}$, the probability of $Q_{\rm mor}\gtrsim 0.2$ is higher than 90\%, which implies that the degree of morphological quenching in GV galaxies might be described by $Q_{\rm mor}\gtrsim 0.2$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The high-cadence survey of Zwicky Transient Facility (ZTF) has completely dominated the discovery of tidal disruption events (TDEs) in the past few years and resulted in the largest sample of TDEs with optical/UV light curves well-sampled around their peaks, providing us an excellent opportunity to construct a peak luminosity function (LF) of tidal disruption flares (TDFs). The new construction is necessary particularly considering that the most updated LF reported in literature has been inferred from only 13 sources from 5 different surveys. Here we present the optical and blackbody LFs calculated by 33 TDFs discovered in the ZTF-I survey. The optical LF can be described by both a power-law profile $dN/dL_g\propto L_g^{-2.3\pm0.2}$, and a Schechter-like function. The blackbody LF can be described by a power-law profile $dN/dL_{\rm bb}\propto L_{\rm bb}^{-2.2\pm0.2}$, shallower than the LF made of previous van Velzen (2018) sample. A possible low-luminosity turnover in the optical LF supports an Eddington-limited emission scenario. The drop of volumetric rate at high luminosity suggests a rate suppression due to direct captures of the black hole. The total volumetric rate is one order of magnitude lower than the previous estimation, which is probably not simply caused by the high fraction post-peak sources (7/13) in the previous sample. Instead, the normalization step during the previous LF construction to reconcile various surveys might adversely amplify the influence of serendipitous discoveries. Therefore, TDFs selected from ongoing and upcoming uniform surveys like ZTF, Vera Rubin Observatory (VRO) and Wide-Field Survey Telescope (WFST) should yield more accurate LFs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jingjing Shi
Yingjie Peng
Benedikt Diemer
Adam R. H. Stevens
Annalisa Pillepich
Alvio Renzini
Jing Dou
Yu Gao
Qiusheng Gu
Luis C. Ho
Xu Kong
Claudia del P. Lagos
Di Li
Jiaxuan Li
Roberto Maiolino
Filippo Mannucci
Lizhi Xie
Chengpeng Zhang
摘要： Black hole feedback has been widely implemented as the key recipe to quench star formation in massive galaxies in modern semi-analytic models and hydrodynamical simulations. As the theoretical details surrounding the accretion and feedback of black holes continue to be refined, various feedback models have been implemented across simulations, with notable differences in their outcomes. Yet, most of these simulations have successfully reproduced some observations, such as stellar mass function and star formation rate density in the local Universe. We use the recent observation on the change of neutral hydrogen gas mass (including both ${\rm H_2}$ and ${\rm HI}$) with star formation rate of massive central disc galaxies as a critical constraint of black hole feedback models across several simulations. We find that the predictions of IllustrisTNG agree with the observations much better than the other models tested in this work. This favors IllustrisTNG's treatment of active galactic nuclei - where kinetic winds are driven by black holes at low accretion rates - as more plausible amongst those we test. In turn, this also indirectly supports the idea that the massive central disc galaxy population in the local Universe was likely quenched by AGN feedback.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xinwen Shu
Lei Yang
Daizhong Liu
Wei-Hao Wang
Tao Wang
Yunkun Han
Xingxing Huang
Chen-Fatt Lim
Yu-Yen Chang
Wei Zheng
Xianzhong Zheng
Junxian Wang
Xu Kong
摘要： We present ALMA 870um and JCMT SCUBA2 850um dust continuum observations of a sample of optically dark and strongly lensed galaxies in the cluster fields. The ALMA and SCUBA2 observations reach a median rms of about 0.11 mJy and 0.44 mJy, respectively, with the latter close to the confusion limit of the data at 850um. This represents one of the most sensitive searches for dust emission in optically dark galaxies. We detect the dust emission in 12 out of 15 galaxies at >3.8 sigma, corresponding to a detection rate of 80 per cent. Thanks to the gravitational lensing, our observations reach a deeper limiting flux than previous surveys in blank fields by a factor of 3. We estimate delensed infrared luminosities in the range log(LIR)=11.5-12.7 Lsun, which correspond to dust-obscured star formation rates (SFRs) of 30 to 520 Msun per year. Stellar population fits to the optical-to-NIR photometric data yield a median redshift z=4.26 and de-lensed stellar mass log(Mstar)=10.78 Msun. They contribute a lensing-corrected star-formation rate density at least an order of magnitude higher than that of equivalently massive UV-selected galaxies at z>3. The results suggest that there is a missing population of massive star-forming galaxies in the early Universe, which may dominate the SFR density at the massive end. Five optically dark galaxies are located within r99.974% from Poisson statistics. Follow-up spectroscopic observations with ALMA and JWST are crucial to confirm whether it is associated with a protocluster at similar redshifts.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Low-mass compact stellar systems (CSSs; $M_{\star}$ $<$ 10$^{10}$ M$_{\odot}$) are thought to be a mixed bag of objects with various formation mechanisms. Previous surveys of CSSs were biased to relatively high-density environments and cannot provide a complete view of the environmental dependence of the formation of CSSs. We conduct the first-ever unbiased flux-limited census of nearby quiescent CSSs over a total sky area of $\sim$ 200 deg$^{2}$ observed by the GAMA spectroscopic survey. The complete sample includes 82 quiescent CSSs, of which 85\% fall within the stellar mass range of classical compact ellipticals (cEs).\ By quantifying the local environment with the normalized projected distance $D/R_{\rm vir}$ to the nearest luminous neighboring galaxy, we find that these CSSs have a bimodal $D/R_{\rm vir}$ distribution, with one group peaking near $\sim$ 0.1$\times$$R_{\rm vir}$ (satellite) and the other peaking near $\sim$ 10$\times$$R_{\rm vir}$ (field). In contrast to the CSSs, ordinary quiescent galaxies of similar masses have unimodal $D/R_{\rm vir}$ distribution.\ Satellite CSSs are older and more metal-rich than field CSSs on average. The bimodal $D/R_{\rm vir}$ distribution of quiescent CSSs reinforces the existence of two distinct formation channels (tidal stripping and born-to-be) for cEs and may be understood in two mutually inclusive perspectives, i.e., substantial tidal stripping happens only when satellite galaxies travel sufficiently close to their massive hosts, and there exists an excess of high-density cE-bearing subhalos close to massive halos.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Expected to be of the highest survey power telescope in the northern hemisphere, the Wide Field Survey Telescope (WFST) will begin its routine observations of the northern sky since 2023. WFST will produce a lot of scientific data to support the researches of time-domain astronomy, asteroids and the solar system, galaxy formation and cosmology and so on. We estimated that the 5 $\sigma$ limiting magnitudes of WFST with 30 second exposure are $u=22.31$ mag, $g=23.42$ mag, $r=22.95$ mag, $i=22.43$ mag, $z=21.50$ mag, $w=23.61$ mag. The above values are calculated for the conditions of $airmass=1.2$, seeing = 0.75 arcsec, precipitable water vapour (PWV) = 2.5 mm and Moon-object separation = $45^{\circ}$ at the darkest New Moon night of the Lenghu site (V=22.30 mag, Moon phase $\theta=0^{\circ}$). The limiting magnitudes in different Moon phase conditions are also calculated. The calculations are based on the empirical transmittance data of WFST optics, the vendor provided CCD quantum efficiency, the atmospherical model transmittance and spectrum of the site. In the absence of measurement data such as sky transmittance and spectrum, we use model data.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Expected to be of the highest survey power telescope in the northern hemisphere, the Wide Field Survey Telescope (WFST) will begin its routine observations of the northern sky since 2023. WFST will produce a lot of scientific data to support the researches of time-domain astronomy, asteroids and the solar system, galaxy formation and cosmology and so on. We estimated that the 5 $\sigma$ limiting magnitudes of WFST with 30 second exposure are $u=22.31$ mag, $g=23.42$ mag, $r=22.95$ mag, $i=22.43$ mag, $z=21.50$ mag, $w=23.61$ mag. The above values are calculated for the conditions of $airmass=1.2$, seeing = 0.75 arcsec, precipitable water vapour (PWV) = 2.5 mm and Moon-object separation = $45^{\circ}$ at the darkest New Moon night of the Lenghu site (V=22.30 mag, Moon phase $\theta=0^{\circ}$). The limiting magnitudes in different Moon phase conditions are also calculated. The calculations are based on the empirical transmittance data of WFST optics, the vendor provided CCD quantum efficiency, the atmospherical model transmittance and spectrum of the site. In the absence of measurement data such as sky transmittance and spectrum, we use model data.
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