Low-mass Spirals Research Articles

The diversity of spiral galaxies explained

ABSTRACT An extensive catalogue of spatially resolved galaxy rotation curves (RCs) and multiband optical light profiles for 1752 observed spiral galaxies is assembled to explore the drivers of diversity in galaxy structural parameters, RC shapes, and stellar mass profiles. Similar data were extracted from the ‘Numerical Investigation of a Hundred Astrophysical Objects’ galaxy simulations to identify any differences between observations and simulations. Several parameters, including the inner slope $\mathcal {S}$ of a RC, were tested for diversity. Two distinct populations are found in observed and simulated galaxies: (i) blue, low-mass spirals with stellar mass M⋆ ≲ 109.3 M⊙ and roughly constant $\mathcal {S}$; and (ii) redder, more massive and more diverse spirals with rapidly increasing $\mathcal {S}$. In all cases, the value of $\mathcal {S}$ seems equally contributed by the baryonic and non-baryonic (dark) matter. Diversity is shown to increase mildly with mass. Numerical simulations reproduce well most baryon-dominated galaxy parameter distributions, such as the inner stellar mass profile slope and baryonic scaling relations, but they struggle to match the full diversity of observed galaxy RCs (through $\mathcal {S}$) and most dark matter-dominated parameters. To reproduce observations, the error broadening of the simulation’s intrinsic spread of RC metrics would have to be tripled. The differences in various projections of observed and simulated scaling relations may reflect limitations of current subgrid physics models to fully capture the complex nature of galaxies. For instance, active galactic nuclei (AGNs) are shown to have a significant effect on the shapes of simulated RCs. The inclusion of AGN feedback brings simulated and observed inner RC shapes into closer agreement.

SDSS-IV MaNGA: 3D spin alignment of spiral and S0 galaxies

ABSTRACT We investigate the 3D spin alignment of galaxies with respect to the large-scale filaments using the MaNGA survey. The cosmic web is reconstructed from the Sloan Digital Sky Survey using disperse and the 3D spins of MaNGA galaxies are estimated using the thin disc approximation with integral field spectroscopy kinematics. Late-type spiral galaxies are found to have their spins parallel to the closest filament’s axis. The alignment signal is found to be dominated by low-mass spirals. Spins of S0-type galaxies tend to be oriented preferentially in perpendicular direction with respect to the filament’s axis. This orthogonal orientation is found to be dominated by S0s that show a notable misalignment between their kinematic components of stellar and ionized gas velocity fields and/or by low-mass S0s with lower rotation support compared to their high-mass counterparts. Qualitatively similar results are obtained when splitting galaxies based on the degree of ordered stellar rotation, such that galaxies with high spin magnitude have their spin aligned, and those with low spin magnitude in perpendicular direction to the filaments. In the context of conditional tidal torque theory, these findings suggest that galaxies’ spins retain memory of their larger scale environment. In agreement with measurements from hydrodynamical cosmological simulations, the measured signal at low redshift is weak, yet statistically significant. The dependence of the spin-filament orientation of galaxies on their stellar mass, morphology, and kinematics highlights the importance of sample selection to detect the signal.

SDSS-IV MaNGA: the ‘G-dwarf problem’ revisited

ABSTRACT The levels of heavy elements in stars are the product of enhancement by previous stellar generations, and the distribution of this metallicity among the population contains clues to the process by which a galaxy formed. Most famously, the ‘G-dwarf problem’ highlighted the small number of low-metallicity G-dwarf stars in the Milky Way, which is inconsistent with the simplest picture of a galaxy formed from a ‘closed box’ of gas. It can be resolved by treating the Galaxy as an open system that accretes gas throughout its life. This observation has classically only been made in the Milky Way, but the availability of high-quality spectral data from SDSS-IV MaNGA and the development of new analysis techniques mean that we can now make equivalent measurements for a large sample of spiral galaxies. Our analysis shows that high-mass spirals generically show a similar deficit of low-metallicity stars, implying that the Milky Way’s history of gas accretion is common. By contrast, low-mass spirals show little sign of a G-dwarf problem, presenting the metallicity distribution that would be expected if such systems evolved as pretty much closed boxes. This distinction can be understood from the differing timescales for star formation in galaxies of differing masses.

Passive spirals and shock influenced star formation in the merging cluster A3376

ABSTRACT We present a detailed analysis of star formation properties of galaxies in a nearby (z ∼ 0.046) young (∼0.6 Gyr) post-merger cluster system A3376, with a moderate merger shock front (vs ∼1630 km s−1; $\mathcal {M}$ ∼ 2) observed as symmetric radio relics. Exploiting the spectroscopic data from the wide-field OmegaWINGS survey and the associated photometric information, our investigations reveal the plausible effects of the dynamic post-merger environment differing from the high-density cluster environment experienced prior to the merging activity. The remnants of the pre-merger relaxed cluster environment are realized through the existence of passive spiral galaxies located in the central regions of the cluster between the two brightest cluster galaxies. We discover A3376 to contain a population of massive (log (M*/M⊙) > 10) blue regular star-forming spirals in regions of maximum merger shock influence but exhibiting star formation rates similar to those in relaxed clusters at similar epoch. We further discover low-mass (log (M*/M⊙) ≤ 10) late-type blue post-starburst galaxies which could either be formed as a result of rapid quenching of low-mass spirals following the shock-induced star formation or due to the intense surge in the intracluster medium pressures at the beginning of the merger. With the possibility of the merger shock affecting high- and low-mass spirals differently, our results bridge the seemingly contradictory results observed in known merging cluster systems so far and establish that different environmental effects are at play right from pre- to post-merger stages.

DRIVERS OF H I TURBULENCE IN DWARF GALAXIES

Neutral hydrogen (HI) velocity dispersions are believed to be set by turbulence in the interstellar medium (ISM). Although turbulence is widely believed to be driven by star formation (SF), recent studies have shown that this driving mechanism may not be dominant in regions of low SF rate surface density (SFRSD), such as found in dwarf galaxies or the outer regions of spirals. We have generated average HI line profiles in a number of nearby dwarfs and low-mass spirals by co-adding HI spectra in regions with either a common radius or SFRSD. We find that the spatially-resolved superprofiles are composed of a central narrow peak (5-15 km/s) with higher velocity wings to either side. With the assumption that the central peak reflects the turbulent velocity dispersion, we compare HI kinematics to local ISM properties, including surface mass densities and measures of SF. The HI velocity dispersion is correlated most strongly with surface mass density, which points at a gravitational origin for turbulence, but it is unclear which instabilities can operate efficiently in these systems. SF energy is produced at a level sufficient to drive HI turbulent motions where SFRSD > 10^-4 Msun yr^-1 kpc^-2. At low SF intensities, SF does not supply enough energy for turbulence, nor does it uniquely determine the velocity dispersion. Nevertheless, SF appears to provide a lower threshold for HI velocity dispersions. We find that coupling efficiency decreases with increasing SFRSD, consistent with a picture where SF couples to the ISM with constant efficiency, but that less of that energy is found in HI at higher SFRSD. We examine a number of potential drivers of HI turbulence, including SF, gravitational instabilities, the magnetorotational instability, and accretion, and find that no single mechanism can drive the observed levels of turbulence at low SFRSD. We discuss possible solutions to this conundrum.

LOCAL BENCHMARKS FOR THE EVOLUTION OF MAJOR-MERGER GALAXIES—SPITZEROBSERVATIONS OF AK-BAND SELECTED SAMPLE

We present Spitzer observations for a sample of close major-merger galaxy pairs (KPAIR sample) selected from cross-matches between the Two Micron All Sky Survey and Sloan Digital Sky Survey Data Release 3. The goals are to study the star formation activity in these galaxies and to set a local bench mark for the cosmic evolution of close major mergers. The Spitzer KPAIR sample (27 pairs, 54 galaxies) includes all spectroscopically confirmed spiral–spiral (S+S) and spiral–elliptical (S+E) pairs in a parent sample that is complete for primaries brighter than K = 12.5 mag, projected separations of 5 h−1 kpc ⩽ s ⩽ 20 h−1 kpc, and mass ratios ⩽2.5. The Spitzer data, consisting of images in seven bands (3.6, 4.5, 5.8, 8, 24, 70, 160 μm), show very diversified IR emission properties. Compared to single spiral galaxies in a control sample, only spiral galaxies in S+S pairs show significantly enhanced specific star formation rate (sSFR = SFR/M), whereas spiral galaxies in S+E pairs do not. Furthermore, the SFR enhancement of spiral galaxies in S+S pairs is highly mass-dependent. Only those with M ≳ 1010.5 M☉ show significant enhancement. Relatively low-mass (M ∼ 1010 M☉) spirals in S+S pairs have about the same SFR/M compared to their counterparts in the control sample, while those with 1011 M☉ have on average a ∼3 times higher SFR/M than single spirals. There is evidence for a correlation between the global star formation activities (but not the nuclear activities) of the component galaxies in massive S+S major-merger pairs (the "Holmberg effect"). There is no significant difference in the SFR/M between the primaries and the secondaries, nor between spirals of SEP < 1 and those of SEP ⩾ 1, SEP being the normalized separation parameter. The contribution of KPAIR galaxies to the cosmic SFR density in the local universe is only 1.7%, and amounts to .

MODELING THE GRB HOST GALAXY MASS DISTRIBUTION: ARE GRBs UNBIASED TRACERS OF STAR FORMATION?

We model the mass distribution of long gamma-ray burst (GRB) host galaxies given recent results suggesting that GRBs occur in low metallicity environments. By utilizing measurements of the redshift evolution of the mass-metallicity (M-Z) relationship for galaxies, along with a sharp host metallicity cut-off suggested by Modjaz and collaborators, we estimate an upper limit on the stellar mass of a galaxy that can efficiently produce a GRB as a function of redshift. By employing consistent abundance indicators, we find that sub-solar metallicity cut-offs effectively limit GRBs to low stellar mass spirals and dwarf galaxies at low redshift. At higher redshifts, as the average metallicity of galaxies in the Universe falls, the mass range of galaxies capable of hosting a GRB broadens, with an upper bound approaching the mass of even the largest spiral galaxies. We compare these predicted limits to the growing number of published GRB host masses and find that extremely low metallicity cut-offs of 0.1 to 0.5 solar are effectively ruled out by a large number of intermediate mass galaxies at low redshift. A mass function that includes a smooth decrease in the efficiency of producing GRBs in galaxies of metallicity above 12+log(O/H)_(KK04) ~ 8.7 can, however, accommodate a majority of the measured host galaxy masses. We find that at z ~ 1, the peak in the observed GRB host mass distribution is inconsistent with the expected peak in the mass of galaxies harboring most of the star formation. This suggests that GRBs are metallicity biased tracers of star formation at low and intermediate redshifts, although our model predicts that this bias should disappear at higher redshifts due to the evolving metallicity content of the universe.

An Offset Seyfert 2 Nucleus in the Minor Merger System NGC 3341

We present the discovery of a triplet of emission-line nuclei in the disturbed disk galaxy NGC 3341, based on archival data from the Sloan Digital Sky Survey and new observations from the Keck Observatory. This galaxy contains two offset nuclei within or projected against its disk, at projected distances of 5.1 and 8.4 kpc from its primary nucleus and at radial velocity separation of less than 200 km s−1 from the primary. These appear to be either dwarf ellipticals or the bulges of low-mass spirals whose disks have already been stripped off while merging into the primary galaxy. The inner offset nucleus has a Seyfert 2 spectrum and a stellar velocity dispersion of 70 ± 7 km s−1. The outer offset nucleus has very weak emission lines consistent with a LINER classification, and the primary nucleus has an emission-line spectrum close to the boundary between LINER/H II composite systems and H II nuclei; both may contain accreting massive black holes, but the optical classifications alone are ambiguous. The detection of an offset active nucleus in NGC 3341 provides a strong suggestion that black hole accretion episodes during minor mergers can be triggered in the nuclei of dwarf secondary galaxies as well as in the primary.

Outside-In Disk Evolution in the Large Magellanic Cloud

From the analysis of the color-magnitude diagrams and color functions of four wide LMC fields located from 2 to 6 kpc from the kinematic center of the LMC we present evidence that, while the oldest population is coeval in all fields, the age of the youngest component of the dominant stellar population gradually increases with galactocentric distance, from currently active star formation in a field at 2.3°, to 100 Myr, 0.8 Gyr, and 1.5 Gyr in fields at 4.0°, 5.5°, and 7.1°, respectively. This outside-in quenching of the star formation in the LMC disk is correlated with the decreasing H I column density (which is ≤2 × 1020 cm−2 in the two outermost fields with little or no current star formation). Other work in the literature hints at similar behavior in the stellar populations of irregular galaxies and in M33. This is observational evidence against the inside-out disk formation scenario in low-mass spirals and irregular galaxies. Alternatively, it could be that the age distribution with radius results from interplay between the evolution with time of the star-forming area of the LMC and the subsequent outward migration of the stars.

The Nature of Nearby Counterparts to Intermediate‐Redshift Luminous Compact Blue Galaxies. III. Interferometric Observations of Neutral Atomic and Molecular Gas

We present the results of a VLA and OVRO-MMA follow-up to our single-dish surveys of the neutral atomic and molecular gas in a sample of nearby Luminous Compact Blue Galaxies (LCBGs). These luminous, blue, high surface brightness, starbursting galaxies were selected using criteria similar to that used to define LCBGs at higher redshifts. The surveys were undertaken to study the nature and evolutionary possibilities of LCBGs, using dynamical masses and gas depletion time scales as constraints. Here we present nearly resolved VLA H I maps of four LCBGs, as well as results from the literature for a fifth LCBG. In addition, we present OVRO-MMA maps of CO(J=1-0) in two of these LCBGs. We have used the resolved H I maps to separate the H I emission from target galaxies and their companions to improve the accuracy of our gas and dynamical mass estimates. For this sub-sample of LCBGs, we find that the dynamical masses measured with the single-dish telescope and interferometer are in agreement. However, we find that we have overestimated the mass of H I in two galaxies by a significant amount, possibly as much as 75%, when compared to the single-dish estimates. These two galaxies have companions within a few arc minutes; we find that our single-dish and interferometric measurements of H I masses are in reasonable agreement for galaxies with more distant companions. The H I velocity fields indicate that all five galaxies are clearly rotating yet distorted, likely due to recent interactions. Our measurements of the gas and dynamical masses of LCBGs point towards evolution into low mass galaxies such as dwarf ellipticals, irregulars, and low mass spirals, consistent with studies of LCBGs at higher redshifts.

Evolution of Field Spiral Galaxies up to Redshiftsz= 1

We have gained intermediate-resolution spectroscopy with the FORS instruments of the Very Large Telescope (VLT) and high-resolution imaging with the Advanced Camera for Surveys aboard HST for a sample of 220 distant field spiral galaxies within the FORS Deep Field and William Herschel Deep Field. Spatially resolved rotation curves were extracted and fitted with synthetic velocity fields that take into account all geometric and observational effects, such as blurring due to the slit width and seeing influence. Using these fits, the maximum rotation velocity Vmax could be determined for 124 galaxies that cover the redshift range 0.1 < z < 1.0 and comprise a variety of morphologies from early-type spirals to very late types and irregulars. The luminosity-rotation velocity distribution of this sample, which represents an average look-back time of ~5 Gyr, is offset from the Tully-Fisher relation (TFR) of local low-mass spirals, whereas the distant high-mass spirals are compatible with the local TFR. Taking the magnitude-limited character of our sample into account, we show that the slope of the local and the intermediate- z TFR would be in compliance if its scatter decreased by more than a factor of 3 between z ≈ 0.5 and 0. Accepting this large evolution of the TFR scatter, we hence find no strong evidence for a mass- or luminosity-dependent evolution of disk galaxies. On the other hand, we derive stellar mass-to-luminosity ratios (M/L) that indicate a luminosity-dependent evolution in the sense that distant low-luminosity disks have much lower M/L than their local counterparts, while high-luminosity disks barely evolved in M/L over the covered redshift range. This could be the manifestation of the "downsizing" effect, i.e., the successive shift of the peak of star formation from high-mass to low-mass galaxies toward lower redshifts. This trend might be canceled out in the TF diagram due to the simultaneous evolution of multiple parameters. We also estimate the ratios between stellar and total masses, finding that these remained constant since z = 1, as would be expected in the context of hierarchically growing structure.

The Evolution of Disk Galaxy Scaling Relations Since Redshift z = 1

AbstractBased on VLT/FORS spectroscopy and HST/ACS imaging, we have constructed a sample of 125 field spiral galaxies that cover redshifts up to z = 1. By deriving the galaxies' luminosities, disk sizes, maximum rotation velocities, stellar masses, total masses, gas-phase metallicities etc., we are able to study the evolution of fundamental scaling relations like the Tully–Fisher relation as a function of cosmic time. While the evolution of most of the galaxies' fundamental parameters is in compliance with a hierarchical structure growth, the results from stellar population modelling favour a down-sizing scenario in the sense that the average stellar ages in high-mass spirals are older than in low-mass spirals.

The Tully-Fisher relation at intermediate redshift

Using the Very Large Telescope in Multi Object Spectroscopy mode, we have observed a sample of 113 field spiral galaxies in the FORS Deep Field (FDF) with redshifts in the range . The galaxies were selected based on apparent brightness () and encompass all late spectrophotometric types from Sa to Sdm/Im. Spatially resolved rotation curves have been extracted for 77 galaxies and fitted with synthetic velocity fields taking into account all observational effects from inclination and slit misalignment to seeing and slit width. We also compared different shapes for the intrinsic rotation curve. To obtain robust values of Vmax, our analysis is focused on galaxies with rotation curves that extend well into the region of constant rotation velocity at large radii. If the slope of the local Tully-Fisher relation (TFR) is held fixed, we find evidence for a mass-dependent luminosity evolution which is as large as up to for the lowest-mass galaxies, but is small or even negligible for the highest-mass systems in our sample. In effect, the TFR slope is shallower at in comparison to the local sample. We argue for a mass-dependent evolution of the mass-to-light ratio. An additional population of blue, low-mass spirals does not seem a very appealing explanation. The flatter tilt we find for the distant TFR is in contradiction to the predictions of recent semi-analytic simulations.

Scaling Relations of Field Spirals at intermediate Redshift

In the last few years, galaxies at redshifts up to z~1 have become accessible for medium-resolved spectroscopy thanks to the new generation of 10m-class telescopes. With kinematic and photometric information on spiral galaxies in this regime, well-known scaling relations like the Tully-Fisher relation (TFR) can be studied over half a Hubble time. By comparison to local samples, these studies facilitate simultaneous tests of the hierarchical merging scenario and stellar population models. Using the Very Large Telescope, we obtained spatially resolved rotation curves of 78 spiral galaxies in the FORS Deep Field (FDF), covering all Hubble types from Sa to Sm/Irr at redshifts 0.1<z<1.0. We find evidence for a B-band luminosity increase of up to 2mag for low-mass spirals, whereas the most massive galaxies are of the same luminosity as their local counterparts. In effect, the TFR slope decreases significantly. This would explain the discrepant results of previous observational studies. We also present the velocity-size relation and compare it to the predictions of numerical simulations based on the hierarchical merging scenario.

The Star Formation Properties of Disk Galaxies: Hα Imaging of Galaxies in the Coma Supercluster

We present integrated Hα measurements obtained from imaging observations of 98 late-type galaxies, primarily selected in the Coma supercluster. These data, combined with Hα photometry from the literature, include a magnitude-selected sample of spiral (Sa to Irr) galaxies belonging to the Wall complete up to mp = 15.4, and thus composed of galaxies brighter than Mp = -18.8 (H0 = 100 km s-1 Mpc-1). The frequency distribution of the Hα equivalent width, determined for the first time from an optically complete sample, is approximately Gaussian, peaking at EW ~ 25 A. We find that, at the present limiting luminosity, the star formation properties of spiral + Irr galaxy members of the Coma and A1367 Clusters do not differ significantly from those of the isolated ones belonging to the Great Wall. The present analysis confirms the well-known increase of the current massive star formation rate (SFR) with Hubble type. Moreover, perhaps a more fundamental anticorrelation exists between the SFR and the mass of disk galaxies: low-mass spirals and dwarf have present SFRs ~50 times higher than giant spirals. This result is consistent with the idea that disk galaxies are coeval, evolving as closed systems with exponentially declining SFR, and that the mass of their progenitor protogalaxies is the principal parameter governing their evolution. Massive having high initial efficiency of collapse, or a short collapse timescale, have retained little gas to feed the present epoch of star formation. These findings support the conclusions of Gavazzi & Scodeggio, who studied the color-mass relation of a local galaxy sample, and agree with the analysis by Cowie et al., who traced the star formation history of galaxies up to z > 1.