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Register a new userMultiple Mechanisms Quench Passive Spiral Galaxies
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Amelia Fraser-McKelvie
Publication date
2017
fields
Physics
and research's language is
English
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We examine the properties of a sample of 35 nearby passive spiral galaxies in order to determine their dominant quenching mechanism(s). All five low mass ($textrm{M}_{star} < 1 times 10^{10} textrm{M}_{odot}$) passive spiral galaxies are located in the rich Virgo cluster. This is in contrast to low mass spiral galaxies with star formation, which inhabit a range of environments. We postulate that cluster-scale gas stripping and heating mechanisms operating only in rich clusters are required to quench low mass passive spirals, and ram-pressure stripping and strangulation are obvious candidates. For higher mass passive spirals, while trends are present, the story is less clear. The passive spiral bar fraction is high: 74$pm$15%, compared with 36$pm$5% for a mass, redshift, and T-type matched comparison sample of star forming spiral galaxies. The high mass passive spirals occur mostly, but not exclusively, in groups, and can be central or satellite galaxies. The passive spiral group fraction of 74$pm$15% is similar to that of the comparison sample of star forming galaxies at 61$pm$7%. We find evidence for both quenching via internal structure and environment in our passive spiral sample, though some galaxies have evidence of neither. From this, we conclude no one mechanism is responsible for quenching star formation in passive spiral galaxies - rather, a mixture of mechanisms are required to produce the passive spiral distribution we see today.
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We have identified a population of passive spiral galaxies from photometry and integral field spectroscopy. We selected z<0.035 spiral galaxies that have WISE colours consistent with little mid-infrared emission from warm dust. Matched aperture photometry of 51 spiral galaxies in ultraviolet, optical and mid-infrared show these galaxies have colours consistent with passive galaxies. Six galaxies form a spectroscopic pilot study and were observed using the Wide-Field Spectrograph (WiFeS) to check for signs of nebular emission from star formation. We see no evidence of substantial nebular emission found in previous red spiral samples. These six galaxies possess absorption-line spectra with 4000AA breaks consistent with an average luminosity-weighted age of 2.3 Gyr. Our photometric and IFU spectroscopic observations confirm the existence of a population of local passive spiral galaxies, implying that transformation into early-type morphologies is not required for the quenching of star formation.
We investigate the stellar populations of passive spiral galaxies as a function of mass and environment, using integral field spectroscopy data from the Sydney-AAO Multi-object Integral field spectrograph Galaxy Survey. Our sample consists of $52$ cluster passive spirals and $18$ group/field passive spirals, as well as a set of S0s used as a control sample. The age and [Z/H] estimated by measuring Lick absorption line strength indices both at the center and within $1R_{rm e}$ do not show a significant difference between the cluster and the field/group passive spirals. However, the field/group passive spirals with log(M$_star$/M$_odot)gtrsim10.5$ show decreasing [$alpha$/Fe] along with stellar mass, which is $sim0.1$ dex smaller than that of the cluster passive spirals. We also compare the stellar populations of passive spirals with S0s. In the clusters, we find that passive spirals show slightly younger age and lower [$alpha$/Fe] than the S0s over the whole mass range. In the field/group, stellar populations show a similar trend between passive spirals and S0s. In particular, [$alpha$/Fe] of the field/group S0s tend to be flattening with increasing mass above log(M$_star$/M$_odot)gtrsim10.5$, similar to the field/group passive spirals. We relate the age and [$alpha$/Fe] of passive spirals to their mean infall time in phase-space; we find a positive correlation, in agreement with the prediction of numerical simulations. We discuss the environmental processes that can explain the observed trends. The results lead us to conclude that the formation of the passive spirals and their transformation into S0s may significantly depend on their environments.
In our companion paper (Brought to Light I: Michea et al. 2021), we reveal spectacular spiral galaxy-like features in deep optical imaging of nine Virgo early-type dwarf galaxies, hidden beneath a dominating smooth stellar disk. Using a new combination of approaches, we find that bar- and spiral-like features contribute 2.2-6.4% of the total flux within 2 R$_{rm{eff}}$. In this study, we conduct high resolution simulations of cluster harassment of passive dwarf galaxies. Following close pericenter passages of the cluster core, tidal triggering generates features in our model disks that bear a striking resemblance to the observed features. However, we find the disks must be highly rotationally supported (V$_{rm{peak}}/sigma_0 sim 3$), much higher than typically observed. We propose that some early-type dwarfs may contain a few percent of their mass in a cold, thin disk which is buried in the light of a hot, diffuse disk, and only revealed when they undergo tidal triggering. The red optical colors of our sample do not indicate any recent significant star formation, and our simulations show that very plunging pericenter passages (r$_{rm{peri}}<0.25$r$_{rm{vir}}$) are required for tidal triggering. Thus, many cluster early-type dwarfs with less plunging orbits may host a yet undetected cold stellar disk component. We discuss possible origin scenarios and consider why similar mass star-forming galaxies in the field are significantly more thin disk dominated than in our cluster sample.
This letter studies the formation of azimuthal metallicity variations in the disks of spiral galaxies in the absence of initial radial metallicity gradients. Using high-resolution $N$-body simulations, we model composite stellar discs, made of kinematically cold and hot stellar populations, and study their response to spiral arm perturbations. We find that, as expected, disk populations with different kinematics respond differently to a spiral perturbation, with the tendency for dynamically cooler populations to show a larger fractional contribution to spiral arms than dynamically hotter populations. By assuming a relation between kinematics and metallicity, namely the hotter the population, the more metal-poor it is, this differential response to the spiral arm perturbations naturally leads to azimuthal variations in the mean metallicity of stars in the simulated disk. Thus, azimuthal variations in the mean metallicity of stars across a spiral galaxy are not necessarily a consequence of the reshaping, by radial migration, of an initial radial metallicity gradient. They indeed arise naturally also in stellar disks which have initially only a negative vertical metallicity gradient.
In previous work on galaxy clusters, several authors reported a discovery of an unusual population of galaxies, which have spiral morphologies, but do not show any star formation activity. These galaxies are called ``passive spirals, and have been interesting since it has been difficult to understand the existence of such galaxies. Using a volume limited sample (0.05<z<0.1 and Mr<-20.5; 25813 galaxies) of the Sloan Digital Sky Survey data, we have found 73 (0.28$pm$0.03%) passive spiral galaxies and studied their environments. It is found that passive spiral galaxies live in local galaxy density 1-2 Mpc$^{-2}$ and 1-10 cluster-centric virial radius. Thus the origins of passive spiral galaxies are likely to be cluster related. These characteristic environments coincide with the previously reported environment where galaxy star formation rate suddenly declines and the so-called morphology-density relation turns. It is likely that the same physical mechanism is responsible for all of these observational results. The existence of passive spiral galaxies suggests that a physical mechanism that works calmly is preferred to dynamical origins such as major merger/interaction since such a mechanism can destroy spiral arm structures. Compared with observed cluster galaxy evolution such as the Butcher-Oemler effect and the morphological Butcher-Oemler effect, passive spiral galaxies are likely to be a galaxy population in transition between red, elliptical/S0 galaxies in low redshift clusters and blue, spiral galaxies more numerous in higher redshift clusters.
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