Much of our knowledge of galaxies comes from analysing the radiation emitted by their stars, which depends on the present number of each type of star in the galaxy. The present number depends on the ...stellar initial mass function (IMF), which describes the distribution of stellar masses when the population formed, and knowledge of it is critical to almost every aspect of galaxy evolution. More than 50 years after the first IMF determination, no consensus has emerged on whether it is universal among different types of galaxies. Previous studies indicated that the IMF and the dark matter fraction in galaxy centres cannot both be universal, but they could not convincingly discriminate between the two possibilities. Only recently were indications found that massive elliptical galaxies may not have the same IMF as the Milky Way. Here we report a study of the two-dimensional stellar kinematics for the large representative ATLAS(3D) sample of nearby early-type galaxies spanning two orders of magnitude in stellar mass, using detailed dynamical models. We find a strong systematic variation in IMF in early-type galaxies as a function of their stellar mass-to-light ratios, producing differences of a factor of up to three in galactic stellar mass. This implies that a galaxy's IMF depends intimately on the galaxy's formation history.
We study the volume-limited and nearly mass-selected (stellar mass M
stars 6 × 109 M) ATLAS3D sample of 260 early-type galaxies (ETGs, ellipticals Es and lenticulars S0s). We construct detailed ...axisymmetric dynamical models (Jeans Anisotropic MGE), which allow for orbital anisotropy, include a dark matter halo and reproduce in detail both the galaxy images and the high-quality integral-field stellar kinematics out to about 1R
e, the projected half-light radius. We derive accurate total mass-to-light ratios (M/L)
e
and dark matter fractions f
DM, within a sphere of radius
centred on the galaxies. We also measure the stellar (M/L)stars and derive a median dark matter fraction f
DM = 13 per cent in our sample. We infer masses M
JAM ≡ L × (M/L)
e
2 × M
1/2, where M
1/2 is the total mass within a sphere enclosing half of the galaxy light. We find that the thin two-dimensional subset spanned by galaxies in the
coordinates system, which we call the Mass Plane (MP) has an observed rms scatter of 19 per cent, which implies an intrinsic one of 11 per cent. Here,
is the major axis of an isophote enclosing half of the observed galaxy light, while σ
e
is measured within that isophote. The MP satisfies the scalar virial relation
within our tight errors. This show that the larger scatter in the Fundamental Plane (FP) (L, σ
e
, R
e) is due to stellar population effects including trends in the stellar initial mass function (IMF). It confirms that the FP deviation from the virial exponents is due to a genuine (M/L)
e
variation. However, the details of how both R
e and σ
e
are determined are critical in defining the precise deviation from the virial exponents. The main uncertainty in masses or M/L estimates using the scalar virial relation is in the measurement of R
e. This problem is already relevant for nearby galaxies and may cause significant biases in virial mass and size determinations at high redshift. Dynamical models can eliminate these problems. We revisit the (M/L)
e
-σ
e
relation, which describes most of the deviations between the MP and the FP. The best-fitting relation is
(r band). It provides an upper limit to any systematic increase of the IMF mass normalization with σ
e
. The correlation is more shallow and has smaller scatter for slow rotating systems or for galaxies in Virgo. For the latter, when using the best distance estimates, we observe a scatter in (M/L)
e
of 11 per cent, and infer an intrinsic one of 8 per cent. We perform an accurate empirical study of the link between σ
e
and the galaxies circular velocity V
circ within 1R
e (where stars dominate) and find the relation max (V
circ) 1.76 × σ
e
, which has an observed scatter of 7 per cent. The accurate parameters described in this paper are used in the companion Paper XX (Cappellari et al.) of this series to explore the variation of global galaxy properties, including the IMF, on the projections of the MP.
Galactic archaeology based on star counts is instrumental to reconstruct the past mass assembly of Local Group galaxies. The development of new observing techniques and data reduction, coupled with ...the use of sensitive large field of view cameras, now allows us to pursue this technique in more distant galaxies exploiting their diffuse low surface brightness (LSB) light. As part of the ATLAS3D project, we have obtained with the MegaCam camera at the Canada–France–Hawaii Telescope extremely deep, multiband images of nearby early-type galaxies (ETGs). We present here a catalogue of 92 galaxies from the ATLAS3D sample, which are located in low- to medium-density environments. The observing strategy and data reduction pipeline, which achieve a gain of several magnitudes in the limiting surface brightness with respect to classical imaging surveys, are presented. The size and depth of the survey are compared to other recent deep imaging projects. The paper highlights the capability of LSB-optimized surveys at detecting new prominent structures that change the apparent morphology of galaxies. The intrinsic limitations of deep imaging observations are also discussed, among those, the contamination of the stellar haloes of galaxies by extended ghost reflections, and the cirrus emission from Galactic dust. The detection and systematic census of fine structures that trace the present and past mass assembly of ETGs are one of the prime goals of the project. We provide specific examples of each type of observed structures – tidal tails, stellar streams and shells – and explain how they were identified and classified. We give an overview of the initial results. The detailed statistical analysis will be presented in future papers.
We present new mm interferometric and optical integral-field unit (IFU) observations and construct a sample of 12 elliptical (E) and lenticular (S0) galaxies with molecular gas which have both CO and ...optical maps. The galaxies contain 2 × 107 to 5 × 109 M⊙ of molecular gas distributed primarily in central discs or rings (radii 0.5-4 kpc). The molecular gas distributions are always coincident with distributions of optically obscuring dust that reveal tightly wound spiral structures in many cases. The ionized gas always approximately corotates with the molecular gas, evidencing a link between these two gas components, yet star formation is not always the dominant ionization source. The galaxies with less molecular gas tend to have O iii/Hβ emission-line ratios at high values not expected for star formation. Most E/S0s with molecular gas have young or intermediate-age stellar populations based on optical colours, ultraviolet colours and absorption linestrengths. The few that appear purely old lie close to the limit where such populations would be undetectable based on the mass fractions of expected young to observed old stars. The 8 μm polycyclic aromatic hydrocarbon (PAH) and 24 μm emission yield similar star formation rate (SFR) estimates of E/S0s, but the total infrared overpredicts the rate due to a contribution to dust heating from older stars. The radio-far-infrared relation also has much more scatter than for other star-forming galaxies. However, despite these biases and additional scatter, the derived star formation rates locate the E/S0 galaxies within the large range of the Schmidt-Kennicutt and constant efficiency star formation laws. Thus, the star formation process in E/S0s is not overwhelmingly different than in other star-forming galaxies, although one of the more reliable tracers (24 μm) points to a possible lower star formation efficiency at a given gas surface density.
[C i](1–0) and [C i](2–1) in Resolved Local Galaxies Crocker, Alison F.; Pellegrini, Eric; Smith, J.-D. T. ...
Astrophysical journal/The Astrophysical journal,
12/2019, Letnik:
887, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
We present resolved C
i
line intensities of 18 nearby galaxies observed with the SPIRE FTS spectrometer on the
Herschel Space Observatory
. We use these data along with resolved CO line ...intensities from
J
up
= 1 to 7 to interpret what phase of the interstellar medium the C
i
lines trace within typical local galaxies. A tight, linear relation is found between the intensities of the CO(4–3) and C
i
(2–1) lines; we hypothesize this is due to the similar upper level temperature of these two lines. We modeled the C
i
and CO line emission using large-velocity gradient models combined with an empirical template. According to this modeling, the C
i
(1–0) line is clearly dominated by the low-excitation component. We determine C
i
to molecular mass conversion factors for both the C
i
(1–0) and C
i
(2–1) lines, with mean values of
α
C
i
(1−0)
= 7.3
M
⊙
K
−1
km
−1
s pc
−2
and
α
C
i
(2−1)
= 34
M
⊙
K
−1
km
−1
s pc
−2
with logarithmic root-mean-square spreads of 0.20 and 0.32 dex, respectively. The similar spread of
to
(derived using the CO(2–1) line) suggests that C
i
(1–0) may be just as good a tracer of cold molecular gas as CO(2–1) in galaxies of this type. On the other hand, the wider spread of
α
C
i
(2−1)
and the tight relation found between C
i
(2–1) and CO(4–3) suggest that much of the C
i
(2–1) emission may originate in warmer molecular gas.
We make use of interferometric CO and H i observations, and optical integral-field spectroscopy from the ATLAS3D survey, to probe the origin of the molecular and ionized interstellar medium (ISM) in ...local early-type galaxies. We find that 36 ± 5 per cent of our sample of fast-rotating early-type galaxies have their ionized gas kinematically misaligned with respect to the stars, setting a strong lower limit on the importance of externally acquired gas (e.g. from mergers and cold accretion). Slow rotators have a flat distribution of misalignments, indicating that the dominant source of gas is external. The molecular, ionized and atomic gas in all the detected galaxies are always kinematically aligned, even when they are misaligned from the stars, suggesting that all these three phases of the ISM share a common origin. In addition, we find that the origin of the cold and warm gas in fast-rotating early-type galaxies is strongly affected by environment, despite the molecular gas detection rate and mass fractions being fairly independent of group/cluster membership. Galaxies in dense groups and the Virgo cluster nearly always have their molecular gas kinematically aligned with the stellar kinematics, consistent with a purely internal origin (presumably stellar mass loss). In the field, however, kinematic misalignments between the stellar and gaseous components indicate that at least 42 ± 5 per cent of local fast-rotating early-type galaxies have their gas supplied from external sources. When one also considers evidence of accretion present in the galaxies' atomic gas distributions, ≳46 per cent of fast-rotating field ETGs are likely to have acquired a detectable amount of ISM from accretion and mergers. We discuss several scenarios which could explain the environmental dichotomy, including preprocessing in galaxy groups/cluster outskirts and the morphological transformation of spiral galaxies, but we find it difficult to simultaneously explain the kinematic misalignment difference and the constant detection rate. Furthermore, our results suggest that galaxy mass may be an important independent factor associated with the origin of the gas, with the most massive fast-rotating galaxies in our sample (M
K
≲−24 mag; stellar mass of ≈8 × 1010 M⊙) always having kinematically aligned gas. This mass dependence appears to be independent of environment, suggesting it is caused by a separate physical mechanism.
ABSTRACT
We present the identification of 34 likely binary central stars (CSs) of planetary nebulae (PNe) from Kepler/K2 data, seven of which show eclipses. Of these, 29 are new discoveries. Two ...additional CSs with more complicated variability are also presented. We examined the light curves of all ‘possible’, ‘likely’, and ‘true’ PNe in every Kepler/K2 campaign (0 through 19) to identify CS variability that may indicate a binary CS. For Campaigns 0, 2, 7, 15, and 16, we find 6 likely or confirmed variables among 21 PNe. Our primary effort, though, was focused on Campaign 11 which targeted a Galactic bulge field containing approximately 183 PNe, in which we identified 30 candidate variable CSs. The periods of these variables range from 2.3 h to 30 d, and based on our analysis, most are likely to be close binary star systems. We present periods and preliminary classifications (eclipsing, double degenerate, or irradiated systems) for the likely binaries based on light-curve shape. From our total sample of 204 target PNe, with a correction for incompleteness due to magnitude limits, we calculate a binary fraction of PN central stars to be 20.7 per cent for all the observed PNe, or 23.5 per cent if we limit our sample only to ‘true’ PNe. However, these fractions are almost certainly lower limits due to the large angular size of the Kepler pixels, which leads to reduced sensitivity in detecting variability, primarily as a result of dilution and noise from the nebula and neighbouring stars. We discuss the binary population of CSs based on these results as part of the total known sample of close binary CSs.
We present the < ~1 kpc resolution super(12)CO imaging study of 37 optically selected local merger remnants using new and archival interferometric maps obtained with ALMA, CARMA, the Submillimeter ...Array, and the Plateau de Bure Interferometer. We supplement a sub-sample with single-dish measurements obtained at the Nobeyama Radio Observatory 45 m telescope for estimating the molecular gas mass (10 super(7-11) M sub(middot in circle)) and evaluating the missing flux of the interferometric measurements. Among the sources with robust CO detections, we find that 80% (24/30) of the sample show kinematical signatures of rotating molecular gas disks (including nuclear rings) in their velocity fields, and the sizes of these disks vary significantly from 1.1 kpc to 9.3 kpc. The size of the molecular gas disks in 54% of the sources is more compact than the K-band effective radius. These small gas disks may have formed from a past gas inflow that was triggered by a dynamical instability during a potential merging event. On the other hand, the rest (46%) of the sources have gas disks that are extended relative to the stellar component, possibly forming a late-type galaxy with a central stellar bulge. Our new compilation of observational data suggests that nuclear and extended molecular gas disks are common in the final stages of mergers. This finding is consistent with recent major-merger simulations of gas-rich progenitor disks. Finally, we suggest that some of the rotation-supported turbulent disks observed at high redshifts may result from galaxies that have experienced a recent major merger.
Dust has long been identified as a barrier to measuring inherent galaxy properties. However, the link between dust and attenuation is not straightforward and depends on both the amount of dust and ...its disuibution. Herschel imaging of nearby galaxies undertaken as part of the KINGFISH project allows us to map the dust as seen in emission with unprecedented sensitivity and ~1 kpc resolution. We present here new optical integral field unit spectroscopy for eight of these galaxies that provides complementary 100-200 pc scale maps of the dust attenuation through observation of the reddening in both the Balmer decrement and the stellar continuum. The stellar continuum reddening, which is systematically less than that observed in the Balmer decrement, shows no clear correlation with the dust, suggesting that the distribution of stellar reddening acts as a poor tracer of the overall dust content. The brightest H II regions are observed to be preferentially located in dusty regions, and we do find a correlation between the Balmer line reddening and the dust mass surface density for which we provide an empirical relation. Some of the high-inclination systems in our sample exhibit high extinction, but we also find evidence that unresolved variations in the dust disuibution on scales smaller than 500 pc may contribute to the scatter in this relation. We caution against the use of integrated A sub(V) measures to infer global dust properties.
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