The resolved stellar populations of local galaxies, from which it is possible to derive complete star formation and chemical enrichment histories, provide an important way to study galaxy formation and evolution that is complementary to lookback time studies. We propose to use photometry of resolved stars to measure the star formation histories in a statistical sample of galaxy disks and E/S0 galaxies near their effective radii. These measurements would yield strong evidence to support critical questions regarding the formation of galactic disks and spheroids. The main technological limitation is spatial resolution for photometry in heavily crowded fields, for which we need improvement by a factor of ~10 over what is possible today with filled aperture telescopes.
We combine new data from the main sequence (M_* versus SFR) of star-forming galaxies and galaxy colors (from GALEX to Spitzer) with a flexible stellar population scheme to deduce the mass-to-light ratio (Υ_*) of star-forming galaxies from the SPARC and S^4G samples. We find that the main sequence for galaxies, particular the low-mass end, combined with the locus of galaxy colors, constrains the possible star formation histories of disk and dwarf galaxies to a similar shape found by Speagle et al. (2014). Combining the deduced star formation history with stellar population models in the literat…
We present the delay time distribution (DTD) estimates of Type Ia supernovae (SNe~Ia) using spatially resolved SN~Ia host galaxy spectra from MUSE and MaNGA. By employing a grouping algorithm based on k-means and earth mover's distances (EMD), we separated the host galaxy star formation histories (SFHs) into spatially distinct regions and used maximum likelihood method to constrain the DTD of SNe Ia progenitors. When a power-law model of the form $DTD(t)\propto t^{s} (t>τ)$ is used, we found an SN rate decay slope $s=-1.41^{+0.32}_{-0.33}$ and a delay time $τ=120^{+142}_{-83} Myr$ . Moreover, …
We reexamine the systematic properties of local galaxy populations, using published surveys of star formation, structure, and gas content. After recalibrating star formation measures, we are able to reliably measure specific star formation rates well below the "main sequence" of star formation vs mass. We find an unexpectedly large population of galaxies with star formation rates intermediate between vigorously star-forming main sequence galaxies and passive galaxies, and with gas content disproportionately high for their star formation rates. Several lines of evidence suggest that these quies…
A key task of observational extragalactic astronomy is to determine where -- within galaxies of diverse masses and morphologies -- stellar mass growth occurs, how it depends on galaxy properties and what processes regulate star formation. Using spectroscopic indices derived from the stellar continuum at $\sim 4000$Å, we determine the spatially resolved star-formation histories of 980000 spaxels in 2404 galaxies in the SDSS-IV MaNGA IFU survey. We examine the spatial distribution of star-forming, quiescent, green valley, starburst and post-starburst spaxels as a function of stellar mass and mor…
We analyze the merger and assembly histories of Milky Way (MW) and Andromeda (M31)-like galaxies to quantify how, and how often, disk galaxies of this mass can survive recent major mergers (stellar mass ratio $\ge$ 1:4). For this, we use the cosmological magneto-hydrodynamical simulation TNG50 and identify 198 analog galaxies, selected based on their $z=0$ stellar mass ($10^{10.5-11.2} {\rm M_{\odot}}$), disky stellar morphology and local environment. Firstly, major mergers are common: 85 per cent (168) of MW/M31-like galaxies in TNG50 have undergone at least one major merger across their life…
Spatially resolved star-formation histories of local post-starburst galaxies: Starburst and quenching spatial patterns consistent with recent mergers
University of St Andrews（圣安德鲁斯大学）；University of Edinburgh（爱丁堡大学）；Imperial College London（帝国理工学院）；University of Hertfordshire（赫特福德大学）；Anqing Normal University（安庆师范大学）
We present a detailed study of the Magellanic irregular galaxy NGC 4449 based on both archival and new photometric data from the Legacy Extragalactic UV Survey, obtained with the Hubble Space Telescope Advanced Camera for Surveys and Wide Field Camera 3. Thanks to its proximity ($D=3.82\pm 0.27$ Mpc) we reach stars 3 magnitudes fainter than the tip of the red giant branch in the F814W filter. The recovered star formation history spans the whole Hubble time, but due to the age-metallicity degeneracy of the red giant branch stars, it is robust only over the lookback time reached by our photometr…
We develop and implement an inclination-dependent attenuation prescription for spectral energy distribution (SED) fitting and study its impact on derived star-formation histories. We apply our prescription within the SED fitting code Lightning to a clean sample of 82, z=0.21-1.35 disk-dominated galaxies in the Great Observatories Origins Deep Survey North and South fields. To compare our inclination-dependent attenuation prescription with more traditional fitting prescriptions, we also fit the SEDs with the inclination-independent Calzetti et al. (2000) attenuation curve. From this comparison,…
Searching Within Galaxies for the Earliest Signs of Quenching With Spatially Resolved Star Formation Histories in UVCANDELS Galaxies at z< 0.3
New York City College of Technology（纽约市立学院）；Rutgers University（罗格斯大学）；California Institute of Technology（加州理工学院）；Flatiron Institute Center for Computational Astrophysics（平顶山研究所计算天体物理中心）；University of Chinese Academy of Sciences (UCAS)（中国科学院大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天文与天体物理研究所）；Space Telescope Science Institute（空间望远镜科学研究所）；Arizona State University（亚利桑那州立大学）
Despite decreasing cosmic star formation rate density over the last 10 Gyr, the stellar mass ($M_{*}$) buildups in galaxies were still progressing during this epoch. About 50\% of the current $M_{*}$ density in the universe was built over the last $\sim 8.7$ Gyr. In this research, we investigated the stellar mass buildup and quenching of spatially resolved regions within massive disk galaxies over the last 10 Gyr. We apply the spectral energy distribution (SED) fitting method to SEDs of sub-galactic regions in galaxies to derive the spatially resolved distributions of SFR and $M_{*}$ in the ga…
The role of major mergers in galaxy evolution is investigated through a detailed characterization of the stellar populations, ionized gas properties, and star formation rates (SFR) in the early-stage merger LIRGs IC 1623 W and NGC 6090, by analysing optical Integral Field Spectroscopy (IFS) and high resolution HST imaging. The spectra were processed with the Starlight full spectral fitting code, and the emission lines measured in the residual spectra. The results are compared with control non-interacting spiral galaxies from the CALIFA survey. Merger-induced star formation is extended and rece…
The spatially resolved star formation histories are studied for 32 normal star-forming galaxies drawn from the the Spitzer Extended Disk Galaxy Exploration Science survey. At surface brightness sensitivities fainter than 28 mag arcsec$^{-2}$, the new optical photometry is deep enough to complement archival ultraviolet and infrared imaging and to explore the properties of the emission well beyond the traditional optical extents of these nearby galaxies. Fits to the spectral energy distributions using a delayed star formation history model indicate a subtle but interesting average radial trend f…
This paper presents the spatially resolved star formation history (SFH) of nearby galaxies with the aim of furthering our understanding of the different processes involved in the formation and evolution of galaxies. To this end, we apply the fossil record method of stellar population synthesis to a rich and diverse data set of 436 galaxies observed with integral field spectroscopy in the CALIFA survey. The sample covers a wide range of Hubble types, with stellar masses ranging from $M_\star \sim 10^9$ to $7 \times 10^{11} M_\odot$. Spectral synthesis techniques are applied to the datacubes to …
Modern data empower observers to describe galaxies as the spatially and biographically complex objects they are. We illustrate this through case studies of four, $z\sim1.3$ systems based on deep, spatially resolved, 17-band + G102 + G141 Hubble Space Telescope grism spectrophotometry. Using full spectrum rest-UV/-optical continuum fitting, we characterize these galaxies' observed $\sim$kpc-scale structures and star formation rates (SFRs) and reconstruct their history over the age of the universe. The sample's diversity---passive to vigorously starforming; stellar masses $\log M_*/M_\odot=10.5$…
Aims. Interacting galaxies show unique irregularities in their kinematic structure. By investigating the spatially resolved kinematics and stellar population properties of galaxies that show irregularities, we can paint a detailed picture of the formation and evolutionary processes that took place during its lifetimes. Methods. In this work, we focus on galaxies with a specific kinematic irregularity, a kinematically distinct stellar core (KDC), in particular, counter-rotating galaxies where the core and main body of the galaxy are rotating in opposite directions. We visually identify eleven M…
We study the internal gradients of stellar population properties within $1.5\;R_{\rm e}$ for a representative sample of 721 galaxies with stellar masses ranging between $10^{9}\;M_{\odot}$ to $10^{11.5}\;M_{\odot}$ from the SDSS-IV MaNGA IFU survey. Through the use of our full spectral fitting code FIREFLY, we derive light and mass-weighted stellar population properties and their radial gradients, as well as full star formation and metal enrichment histories. We also quanfify the impact that different stellar population models and full spectral fitting routines have on the derived stellar popu…
We characterize the 3-D spatial variations of [Fe/H], [Mg/H], and [Mg/Fe] in stars at the time of their formation, across 11 simulated Milky Way (MW)- and M31-mass galaxies in the FIRE-2 simulations, to inform initial conditions for chemical tagging. The overall scatter in [Fe/H] within a galaxy decreased with time until $\approx 7$ Gyr ago, after which it increased to today: this arises from a competition between a reduction of azimuthal scatter and a steepening of the radial gradient in abundance over time. The radial gradient is generally negative, and it steepened over time from an initial…
M64 is a nearby spiral galaxy with a Type III anti-truncation component. To trace the origin of the Type III component, we present Hubble Space Telescope/Advanced Camera for Surveys $F606W/F814W$ photometry of resolved stars in a field located in the outer disk ($2.5' \lesssim r \lesssim 6.5'$) of M64. At $r\approx 5.5'$ (7 kpc) to the east, we discover a new metal-poor globular cluster ($R_{\rm eff}=5.73\pm0.02$ pc and $M_V=-9.54\pm0.09$ mag), M64-GC1. This is the first globular cluster found in M64. The color-magnitude diagram (CMD) of the resolved stars in M64-GC1 is well matched by 12 Gyr …
We present a detailed study of the flocculent spiral galaxy NGC 7793, part of the Sculptor group. By analyzing the resolved stellar populations of the galaxy, located at a distance of ~3.7 Mpc, we infer for the first time its radial star formation history (SFH) from Hubble Space Telescope photometry, thanks to both archival and new data from the Legacy ExtraGalactic UV Survey. We determine an average star formation rate (SFR) for the galaxy portion covered by our F555W and F814W data of 0.23 +- 0.02 Msun/yr over the whole Hubble time, corresponding to a total stellar mass of 3.09 +- 0.33 x 10^…
We present a comprehensive study of the applications of the pixel color-magnitude diagram (pCMD) technique for measuring star formation histories (SFHs) and other stellar population parameters of galaxies, and demonstrate that the technique can also constrain distances. SFHs have previously been measured through either the modeling of resolved-star CMDs or of integrated-light SEDs, yet neither approach can easily be applied to galaxies in the "semi-resolved regime". The pCMD technique has previously been shown to have the potential to measure stellar populations and star formation histories in…
Nearby galaxies are the end result of their cosmological evolution, which is predicted to be influenced by the growth of their host dark matter halos. This co-evolution potentially leaves signatures in present-day observed galaxy properties, which might be essential to further understand how the growth and properties of galaxies are connected to those of their host halos. In this work, we study the evolutionary histories of nearby galaxies both in terms of their host halos and the scatter of the star-forming main sequence by investigating their time-resolved stellar populations using absorptio…
L1551 IRS 5 is a FUor-like object located in the Taurus star forming region. We present ALMA 1.3 mm continuum observations using a wide range of baselines. The observations recovered the two circumstellar disks composing the system and, for the first time, resolved the circumbinary ring. We determined the geometry and estimated lower mass limits for the circumstellar disks using simple models. We calculated lower limits for the total mass of both circumstellar disks. After subtracting the two circumstellar disk models from the image, the residuals show a clearly resolved circumbinary ring. Usi…
Stellar kinematics and metallicity are key to exploring formation scenarios for galactic disks and halos. In this work, we characterized the relationship between kinematics and photometric metallicity along the line-of-sight to M31's disk. We combined optical HST/ACS photometry from the Panchromatic Hubble Andromeda Treasury (PHAT) survey with Keck/DEIMOS spectra from the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) survey. The resulting sample of 3512 individual red giant branch stars spans 4-19 projected kpc, making it a useful probe of both the disk and inner…
We present spatially-resolved measurements of star formation histories (SFHs), metallicities, and distances in three nearby elliptical galaxies and the bulge of M31 derived using the pixel color-magnitude diagram (pCMD) technique. We compute pCMDs from archival $\textit{HST}$ photometry of M87, M49, NGC 3377 and M31, and fit the data using the new code $\texttt{PCMDPy}$. We measure distances to each system that are accurate to $\sim 10\%$. The recovered non-parametric SFHs place reasonable ($\pm 1$ dex) constraints on the recent (< 2 Gyr) star formation in M31 and NGC 3377, both of which show …
Planetesimals inevitably bear the signatures of their natal environment, preserving in their composition a record of the metallicity of their system's original gas and dust, albeit one altered by the formation process. When planetesimals are dispersed from their system of origin, this record is carried with them. As each star is likely to contribute at least $10^{12}$ interstellar objects, the Galaxy's drifting population of interstellar objects (ISOs) provides an overview of the properties of its stellar population through time. Using the EAGLE cosmological simulation and models of protoplane…
We present the first dust emission results toward a sample of seven protostellar disk candidates around Class 0 and I sources in the Perseus molecular cloud from the VLA Nascent Disk and Multiplicity (VANDAM) survey with ~0.05'' or 12 AU resolution. To examine the surface brightness profiles of these sources, we fit the Ka-band 8 mm dust-continuum data in the u,v-plane to a simple, parametrized model based on the Shakura-Sunyaev disk model. The candidate disks are well-fit by a model with a disk-shaped profile and have masses consistent with known Class 0 and I disks. The inner-disk surface de…
