Abstract
We study the gas phase metallicity (O/H) and nitrogen abundance gradients traced by star-forming regions in a representative sample of 550 nearby galaxies in the stellar mass range ...109–1011.5 M⊙ with resolved spectroscopic data from the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory survey. Using strong-line ratio diagnostics (R23 and O3N2 for metallicity and N2O2 for N/O) and referencing to the effective (half-light) radius (Re), we find that the metallicity gradient steepens with stellar mass, lying roughly flat among galaxies with log (M⋆/M⊙) = 9.0 but exhibiting slopes as steep as −0.14 dex $R_{\rm e}^{-1}$ at log (M⋆/M⊙) = 10.5 (using R23, but equivalent results are obtained using O3N2). At higher masses, these slopes remain typical in the outer regions of our sample (R > 1.5Re), but a flattening is observed in the central regions (R < 1Re). In the outer regions (R > 2.0Re), we detect a mild flattening of the metallicity gradient in stacked profiles, although with low significance. The N/O ratio gradient provides complementary constraints on the average chemical enrichment history. Unlike the oxygen abundance, the average N/O profiles do not flatten out in the central regions of massive galaxies. The metallicity and N/O profiles both depart significantly from an exponential form, suggesting a disconnect between chemical enrichment and stellar mass surface density on local scales. In the context of inside-out growth of discs, our findings suggest that central regions of massive galaxies today have evolved to an equilibrium metallicity, while the nitrogen abundance continues to increase as a consequence of delayed secondary nucleosynthetic production.
SDSS-IV MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is the largest integral-field unit (IFU) spectroscopy survey to date, aiming to observe a statistically representative sample of ...10,000 low-redshift galaxies. In this paper, we study the reliability of the emission-line fluxes and kinematic properties derived by the MaNGA Data Analysis Pipeline (DAP). We describe the algorithmic choices made in the DAP with regards to measuring emission-line properties, and the effect of our adopted strategy of simultaneously fitting the continuum and line emission. The effects of random errors are quantified by studying various fit-quality metrics, idealized recovery simulations, and repeat observations. This analysis demonstrates that the emission lines are well fit in the vast majority of the MaNGA data set and the derived fluxes and errors are statistically robust. The systematic uncertainty on emission-line properties introduced by the choice of continuum templates is also discussed. In particular, we test the effect of using different stellar libraries and simple stellar-population models on the derived emission-line fluxes and the effect of introducing different tying prescriptions for the emission-line kinematics. We show that these effects can generate large (>0.2 dex) discrepancies at low signal-to-noise ratio and for lines with low equivalent width (EW); however, the combined effect is noticeable even for H EW > 6 . We provide suggestions for optimal use of the data provided by SDSS data release 15 and propose refinements on the DAP for future MaNGA data releases.
The launch of the James Webb Space Telescope (JWST) will open up a new window for observations at the highest redshifts, reaching out to . However, even with this new facility, the first stars will ...remain out of reach, as they are born in small minihalos with luminosities too faint to be detected even by the longest exposure times. In this paper, we investigate the basic properties of the Ultimately Large Telescope, a facility that can detect Population III star formation regions at high redshift. Observations will take place in the near-infrared and therefore a Moon-based facility is proposed. An instrument needs to reach magnitudes as faint as 39 magAB, corresponding to a primary mirror size of about 100 m in diameter. Assuming JWST NIRCam filters, we estimate that Population III sources will have unique signatures in a color-color space and can be identified unambiguously.
To better understand the prevalence of bulgeless galaxies in the nearby field, we dissect giant Sc-Scd galaxies with Hubble Space Telescope (HST) photometry and Hobby-Eberly Telescope (HET) ...spectroscopy. We use the HET High Resolution Spectrograph (resolution R = Delta *l/FWHM 1,000) to measure stellar velocity dispersions in the nuclear star clusters and (pseudo)bulges of the pure-disk galaxies M 33, M 101, NGC 3338, NGC 3810, NGC 6503, and NGC 6946. The dispersions range from 20 ? 1 km s--1 in the nucleus of M 33 to 78 ? 2 km s--1 in the pseudobulge of NGC 3338. We use HST archive images to measure the brightness profiles of the nuclei and (pseudo)bulges in M 101, NGC 6503, and NGC 6946 and hence to estimate their masses. The results imply small mass-to-light ratios consistent with young stellar populations. These observations lead to two conclusions. (1) Upper limits on the masses of any supermassive black holes are M - (2.6 ? 0.5) X 106 M in M 101 and M - (2.0 ? 0.6) X 106 M in NGC 6503. (2) We show that the above galaxies contain only tiny pseudobulges that make up 3% of the stellar mass. This provides the strongest constraints to date on the lack of classical bulges in the biggest pure-disk galaxies. We inventory the galaxies in a sphere of radius 8 Mpc centered on our Galaxy to see whether giant, pure-disk galaxies are common or rare. We find that at least 11 of 19 galaxies with V circ > 150 km s--1, including M 101, NGC 6946, IC 342, and our Galaxy, show no evidence for a classical bulge. Four may contain small classical bulges that contribute 5%-12% of the light of the galaxy. Only four of the 19 giant galaxies are ellipticals or have classical bulges that contribute ~1/3 of the galaxy light. We conclude that pure-disk galaxies are far from rare. It is hard to understand how bulgeless galaxies could form as the quiescent tail of a distribution of merger histories. Recognition of pseudobulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many giant, pure-disk galaxies with no evidence for merger-built bulges? Finally, we emphasize that this problem is a strong function of environment: the Virgo cluster is not a puzzle, because more than 2/3 of its stellar mass is in merger remnants.
By means of a statistical approach that combines different semi-empirical methods of galaxy-halo connection, we derive the stellar-to-halo mass relations (SHMR) of local blue and red central ...galaxies. We also constrain the fraction of halos hosting blue/red central galaxies and the occupation statistics of blue and red satellites as a function of halo mass, Msubh. For the observational input we use the blue and red central/satellite galaxy stellar mass functions and two-point correlation functions in the stellar mass range of 9 < log(Msub */M) < 12. Our results suggest that the SHMR of central galaxies at large masses is shaped by mass quenching. At low masses processes that delay star formation without invoking too strong supernova-driven outflows could explain the high Msub *-to-Msubh ratios of blue centrals as compared to those of the scarce red centrals.
We describe the sample design for the SDSS-IV MaNGA survey and present the final properties of the main samples along with important considerations for using these samples for science. Our target ...selection criteria were developed while simultaneously optimizing the size distribution of the MaNGA integral field units (IFUs), the IFU allocation strategy, and the target density to produce a survey defined in terms of maximizing signal-to-noise ratio, spatial resolution, and sample size. Our selection strategy makes use of redshift limits that only depend on i-band absolute magnitude (Mi), or, for a small subset of our sample, Mi and color (NUV − i). Such a strategy ensures that all galaxies span the same range in angular size irrespective of luminosity and are therefore covered evenly by the adopted range of IFU sizes. We define three samples: the Primary and Secondary samples are selected to have a flat number density with respect to Mi and are targeted to have spectroscopic coverage to 1.5 and 2.5 effective radii (Re), respectively. The Color-Enhanced supplement increases the number of galaxies in the low-density regions of color-magnitude space by extending the redshift limits of the Primary sample in the appropriate color bins. The samples cover the stellar mass range and are sampled at median physical resolutions of 1.37 and 2.5 kpc for the Primary and Secondary samples, respectively. We provide weights that will statistically correct for our luminosity and color-dependent selection function and IFU allocation strategy, thus correcting the observed sample to a volume-limited sample.
Abstract
We measure $\lambda _{R_{\rm e}}$, a proxy for galaxy specific stellar angular momentum within one effective radius, and the ellipticity, ε, for about 2300 galaxies of all morphological ...types observed with integral field spectroscopy as part of the Mapping Nearby Galaxies at Apache Point Observatory survey, the largest such sample to date. We use the $(\lambda _{R_{\rm e}}, \epsilon )$ diagram to separate early-type galaxies into fast and slow rotators. We also visually classify each galaxy according to its optical morphology and two-dimensional stellar velocity field. Comparing these classifications to quantitative $\lambda _{R_{\rm e}}$ measurements reveals tight relationships between angular momentum and galaxy structure. In order to account for atmospheric seeing, we use realistic models of galaxy kinematics to derive a general approximate analytic correction for $\lambda _{R_{\rm e}}$. Thanks to the size of the sample and the large number of massive galaxies, we unambiguously detect a clear bimodality in the $(\lambda _{R_{\rm e}}, \epsilon )$ diagram which may result from fundamental differences in galaxy assembly history. There is a sharp secondary density peak inside the region of the diagram with low $\lambda _{R_{\rm e}}$ and ε < 0.4, previously suggested as the definition for slow rotators. Most of these galaxies are visually classified as non-regular rotators and have high velocity dispersion. The intrinsic bimodality must be stronger, as it tends to be smoothed by noise and inclination. The large sample of slow rotators allows us for the first time to unveil a secondary peak at ±90° in their distribution of the misalignments between the photometric and kinematic position angles. We confirm that genuine slow rotators start appearing above M ≥ 2 × 1011 M⊙ where a significant number of high-mass fast rotators also exist.
The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey is currently acquiring integral-field spectroscopy for the largest sample of galaxies to date. By 2020, the MaNGA Survey-which ...is one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV)-will have observed a statistically representative sample of 104 galaxies in the local universe (z 0.15). In addition to a robust data-reduction pipeline (DRP), MaNGA has developed a data-analysis pipeline (DAP) that provides higher-level data products. To accompany the first public release of its code base and data products, we provide an overview of the MaNGA DAP, including its software design, workflow, measurement procedures and algorithms, performance, and output data model. In conjunction with our companion paper (Belfiore et al.), we also assess the DAP output provided for 4718 observations of 4648 unique galaxies in the recent SDSS Data Release 15 (DR15). These analysis products focus on measurements that are close to the data and require minimal model-based assumptions. Namely, we provide stellar kinematics (velocity and velocity dispersion), emission-line properties (kinematics, fluxes, and equivalent widths), and spectral indices (e.g., D4000 and the Lick indices). We find that the DAP provides robust measurements and errors for the vast majority (>99%) of analyzed spectra. We summarize assessments of the precision and accuracy of our measurements as a function of signal-to-noise. We also provide specific guidance to users regarding the limitations of the data. The MaNGA DAP software is publicly available and we encourage community involvement in its development.
We present a formalism to reveal merging by subtracting the change in the galaxy stellar mass function (MF) due to mass-dependent star formation (SF) from the observed time derivative of the MF. We ...present the SF rate (SFR) in the FORS Deep Field as a function of stellar mass and time spanning image and image. At image, the average SFR is a power law of stellar mass. The average SFR in massive objects at this redshift is 100-500 image yr super(-1). At image, the SFR starts to drop at high masses. The break mass at which the SFR deviates from the power-law form decreases smoothly from image at image to image at image, according to image (downsizing). We directly observe a relationship between SF history and mass. More massive galaxies have steeper and earlier onsets of SF, higher peak SFR, followed by a shorter decay time. The SFR in high-mass galaxies at image can explain their rapid increase in abundance. Within large uncertainties, at most 0.8 effective major mergers per Gyr are consistent with the data, yet enough to transform most high-mass objects into ellipticals contemporaneously with their major SF episode. In contrast, at image and at image, mergers contribute 0.1-0.2 Gyr super(-1) to the increase in number density. This corresponds to image1 major merger per object a image. At image, galaxies are being preferentially destroyed at early times, while at later times the change in their numbers turns positive. This is an indication of the top-down buildup of the red sequence suggested by other recent observations.
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