Abstract
It is generally assumed that galaxies are a bimodal population in both star formation and structure; star-forming galaxies are disks, while passive galaxies host large bulges or are entirely ...spheroidal. Here we test this scenario by presenting a full census of the kinematic morphologies of a volume-limited sample of galaxies in the local universe extracted from the MaNGA galaxy survey. We measure the integrated stellar line-of-sight velocity to velocity dispersion ratio (
V
/
σ
) for 4574 galaxies in the stellar mass range
9.75
<
log
M
⋆
M
⊙
<
11.75
. We show that at fixed stellar mass, the distribution of
V
/
σ
is not bimodal, and that a simple separation between fast and slow rotators is oversimplistic. Fast rotators are a mixture of at least two populations, referred to here as dynamically cold disks and intermediate systems, with disks dominating in both total stellar mass and number. When considering star-forming and passive galaxies separately, the star-forming population is almost entirely made up of disks, while the passive population is mixed, implying an array of quenching mechanisms. Passive disks represent ∼30% (both in number and mass) of passive galaxies, nearly a factor of two higher than that of slow rotators, reiterating that these are an important population for understanding galaxy quenching. These results paint a picture of a local universe dominated by disky galaxies, most of which become somewhat less rotation-supported upon or after quenching. While spheroids are present to a degree, they are certainly not the evolutionary end point for the majority of galaxies.
We investigate the relationship between stellar mass, metallicity and gas content for a magnitude- and volume-limited sample of 260 nearby late-type galaxies in different environments, from isolated ...galaxies to Virgo cluster members. We derive oxygen abundance estimates using new integrated, drift-scan optical spectroscopy and the base metallicity calibrations of Kewley & Ellison (2008, ApJ, 681, 1183). Combining these measurements with ultraviolet to near-infrared photometry and Hi 21 cm line observations, we examine the relations between stellar mass, metallicity, gas mass fraction and star formation rate. We find that, at fixed stellar mass, galaxies with lower gas fractions typically also possess higher oxygen abundances. We also observe a relationship between gas fraction and metal content, whereby gas-poor galaxies are typically more metal-rich, and demonstrate that the removal of gas from the outskirts of spirals may increase the observed average metallicity by ~0.1 dex. Although some cluster galaxies are gas-deficient objects, statistically the stellar-mass metallicity relation is nearly invariant to the environment, in agreement with recent studies. These results indicate that internal evolutionary processes, rather than environmental effects, play a key role in shaping the stellar mass-metallicity relation. In addition, we present metallicity estimates based on observations of 478 nearby galaxies.
Context. Using MegaCam at the CFHT, we obtained a deep narrow band Hα+NII wide-field image of NGC 4569 (M90), the brightest late-type galaxy in the Virgo cluster. The image reveals the presence of ...long tails of diffuse ionized gas, without any associated stellar component extending from the disc of the galaxy up to ≃80 kpc (projected distance) and with a typical surface brightness of a few 10-18 erg s-1 cm-2 arcsec-2. These features provide direct evidence that NGC 4569 is undergoing a ram-presure stripping event. The image also shows a prominent 8 kpc spur of ionized gas that is associated with the nucleus that spectroscopic data identify as an outflow. With some assumptions on the 3D distribution of the gas, we use the Hα surface brightness of these extended low-surface brightness features to derive the density and the mass of the gas that has been stripped during the interaction of the galaxy with the intracluster medium. The comparison with ad hoc chemo-spectrophotometric models of galaxy evolution indicates that the mass of the Hα emitting gas in the tail is a large fraction of that of the cold phase that has been stripped from the disc, suggesting that the gas is ionized within the tail during the stripping process. The lack of star-forming regions suggests that mechanisms other than photoionization are responsible for the excitation of the gas (shocks, heat conduction, magneto hydrodynamic waves). This analysis indicates that ram pressure stripping is efficient in massive (Mstar ≃ 1010.5 M⊙) galaxies located in intermediate-mass (≃1014 M⊙) clusters under formation. It also shows that the mass of gas expelled by the nuclear outflow is only ~1% than that removed during the ram pressure stripping event.Together these results indicate that ram pressure stripping, rather than starvation through nuclear feedback, can be the dominant mechanism that is responsible for the quenching of the star formation activity of galaxies in high density environments.
ABSTRACT We use a volume-, magnitude-limited sample of nearby galaxies to investigate the effect of the environment on the Hi scaling relations. We confirm that the Hi-to-stellar mass ratio ...anticorrelates with stellar mass, stellar mass surface density and NUV -r colour across the whole range of parameters covered by our sample (109M* 1011M,7.5 μ* 9.5Mkpc-2, 2 NUV -r 6mag). These scaling relations are also followed by galaxies in the Virgo cluster, although they are significantly offset towards lower gas content. Interestingly, the difference between field and cluster galaxies gradually decreases moving towards massive, bulge-dominated systems. By comparing our data with the predictions of chemo-spectrophotometric models of galaxy evolution, we show that starvation alone cannot explain the low gas content of Virgo spirals and that only ram-pressure stripping is able to reproduce our findings. Finally, motivated by previous studies, we investigate the use of a plane obtained from the relations between the Hi-to-stellar mass ratio, stellar mass surface density and NUV -r colour as a proxy for the Hi deficiency parameter. We show that the distance from the 'Hi gas fraction plane' can be used as an alternative estimate for the Hi deficiency, but only if carefully calibrated on pre-defined samples of 'unperturbed' systems. PUBLICATION ABSTRACT
•Ti6Al4V, 17-4PH and AlSi10Mg AM alloys have been characterized by multiaxial tests.•Four ductile damage models have been effectively calibrated, showing a good accuracy.•The AM alloys were found to ...have a comparable strength to their not AM homologous.•An appreciable ductility reduction was observed for AM Ti6Al4V and AlSi10Mg.
A great research effort has been spent during the latest years in the characterization of additive manufacturing (AM) alloys, mostly focused on the analysis of microstructure and on the assessment of mechanical strength, especially under high cycle fatigue loads. Post-process treatments have been also investigated, as methods to further improve the AM materials performance. On the contrary, still fewer data are available on AM materials ultimate static strength. The present paper is intended to present a comprehensive experimental and numerical static characterization of Ti6Al4V, 17-4PH, and AlSi10Mg alloys processed via selective laser melting (SLM). A dedicated set of specimen geometries was devised to induce desired multiaxial stress state, and experiments were carried out both on as built and machined AM samples. The results were employed to identify the constitutive behavior of the materials and to calibrate four different ductile damage models. The failure prediction capabilities of the tuned models were thoroughly analyzed and discussed. The overall mechanical properties and the ductility of the investigated alloys were estimated based on the experimental results and on the information provided by the tuned models. Additionally, a comparison with data collected on the corresponding wrought materials, performing the same experiments, was carried out. The results showed a limited reduction of yield and failure strength and a significant reduction in the ductility of AM materials with respect to their wrought counterparts. Moreover, for the less ductile alloys, a weaker dependence of the strain to fracture from the stress state was observed.
The conversion of gas into stars is a fundamental process in astrophysics and cosmology. Stars are known to form from the gravitational collapse of dense clumps in interstellar molecular clouds, and ...it has been proposed that the resulting star formation rate is proportional to either the amount of mass above a threshold gas surface density, or the gas volume density. These star formation prescriptions appear to hold in nearby molecular clouds in our Milky Way Galaxy's disc as well as in distant galaxies where the star formation rates are often much larger. The inner 500 pc of our Galaxy, the Central Molecular Zone (CMZ), contains the largest concentration of dense, high-surface density molecular gas in the Milky Way, providing an environment where the validity of star formation prescriptions can be tested. Here, we show that by several measures, the current star formation rate in the CMZ is an order-of-magnitude lower than the rates predicted by the currently accepted prescriptions. In particular, the region 1° < l < 3°.5, |b| < 0°.5 contains ∼107 M of dense (> several 103 cm−3) molecular gas - enough to form 1000 Orion-like clusters - but the present-day star formation rate within this gas is only equivalent to that in Orion. In addition to density, another property of molecular clouds must be included in the star formation prescription to predict the star formation rate in a given mass of molecular gas. We discuss which physical mechanisms might be responsible for suppressing star formation in the CMZ.
We use a volume-, magnitude-limited sample of nearby galaxies to investigate the effect of the environment on the H i scaling relations. We confirm that the H i-to-stellar mass ratio anticorrelates ...with stellar mass, stellar mass surface density and NUV −r colour across the whole range of parameters covered by our sample (109≲M
*≲ 1011 M⊙, 7.5 ≲μ*≲ 9.5 M⊙ kpc−2, 2 ≲ NUV −r≲ 6 mag). These scaling relations are also followed by galaxies in the Virgo cluster, although they are significantly offset towards lower gas content. Interestingly, the difference between field and cluster galaxies gradually decreases moving towards massive, bulge-dominated systems. By comparing our data with the predictions of chemo-spectrophotometric models of galaxy evolution, we show that starvation alone cannot explain the low gas content of Virgo spirals and that only ram-pressure stripping is able to reproduce our findings. Finally, motivated by previous studies, we investigate the use of a plane obtained from the relations between the H i-to-stellar mass ratio, stellar mass surface density and NUV −r colour as a proxy for the H i deficiency parameter. We show that the distance from the 'H i gas fraction plane' can be used as an alternative estimate for the H i deficiency, but only if carefully calibrated on pre-defined samples of 'unperturbed' systems.
We study the evolution of dwarf (L sub(H) < 10 super(9.6) L sub(H) unk) star-forming and quiescent galaxies in the Virgo Cluster by comparing their UV to radio centimetric properties to the ...predictions of multizone chemospectrophotometric models of galaxy evolution especially tuned to take into account the perturbations induced by the interaction with the cluster intergalactic medium. Our models simulate one or multiple ram pressure stripping events and galaxy starvation. Models predict that all star-forming dwarf galaxies entering the cluster for the first time loose most, if not all, of their atomic gas content, quenching on short timescales ( less than or equal to 150 Myr) their activity of star formation. These dwarf galaxies soon become red and quiescent, gas metal-rich objects with spectrophotometric and structural properties similar to those of dwarf ellipticals. Young, low-luminosity, high surface brightness star-forming galaxies such as late-type spirals and BCDs are probably the progenitors of relatively massive dwarf ellipticals, while it is likely that low surface brightness Magellanic irregulars evolve into very low surface brightness quiescent objects hardly detectable in ground-based imaging surveys. The small number of dwarf galaxies with physical properties intermediate between those of star-forming and quiescent systems is consistent with a rapid (<1 Gyr) transitional phase between the two dwarf galaxy populations. These results, combined with statistical considerations, are consistent with the idea that most of the dwarf ellipticals dominating the faint end of the Virgo luminosity function were initially star-forming systems, accreted by the cluster and stripped of their gas by one or subsequent ram pressure stripping events.
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