This paper describes the Second Public Data Release (DR2) of the Calar Alto Legacy Integral Field Area (CALIFA) survey. The data for 200 objects are made public, including the 100 galaxies of the ...First Public Data Release (DR1). Data were obtained with the integral-field spectrograph PMAS/PPak mounted on the 3.5 m telescope at the Calar Alto observatory. Two different spectral setups are available for each galaxy, (i) a low-resolution V500 setup covering the wavelength range 3745-7500 Angstrom with a spectral resolution of 6.0 Angstrom (FWHM); and (ii) a medium-resolution V1200 setup covering the wavelength range 3650-4840 Angstrom with a spectral resolution of 2.3 Angstrom (FWHM). The sample covers a redshift range between 0.005 and 0.03, with a wide range of properties in the color-magnitude diagram, stellar mass, ionization conditions, and morphological types. All the cubes in the data release were reduced with the latest pipeline, which includes improvedspectrophotometric calibration, spatial registration, and spatial resolution. The spectrophotometric calibration is better than 6% and the median spatial resolution is 2."4. In total, the second data release contains over 1.5 million spectra.
Aims.
There exists some consensus that the stellar mass surface density (Σ
⋆
) and molecular gas mass surface density (Σ
mol
) are the main quantities responsible for locally setting the star ...formation rate. This regulation is inferred from locally resolved scaling relations between these two quantities and the star formation rate surface density (Σ
SFR
), which have been extensively studied in a wide variety of works. However, the universality of these relations is debated. Here, we probe the interplay between these three quantities across different galactic environments at a spatial resolution of 150 pc.
Methods.
We performed a hierarchical Bayesian linear regression to find the best set of parameters
C
⋆
,
C
mol
, and
C
norm
that describe the star-forming plane conformed by Σ
⋆
, Σ
mol
, and Σ
SFR
, such that logΣ
SFR
=
C
⋆
logΣ
⋆
+
C
mol
logΣ
mol
+
C
norm
. We also explored variations in the determined parameters across galactic environments, focusing our analysis on the
C
⋆
and
C
mol
slopes.
Results.
We find signs of variations in the posterior distributions of
C
⋆
and
C
mol
across different galactic environments. The dependence of Σ
SFR
on Σ
⋆
spans a wide range of slopes, with negative and positive values, while the dependence of Σ
SFR
on Σ
mol
is always positive. Bars show the most negative value of
C
⋆
(−0.41), which is a sign of longer depletion times, while spiral arms show the highest
C
⋆
among all environments (0.45). Variations in
C
mol
also exist, although they are more subtle than those found for
C
⋆
.
Conclusions.
We conclude that systematic variations in the interplay of Σ
⋆
, Σ
mol
, and Σ
SFR
across different galactic environments exist at a spatial resolution of 150 pc, and we interpret these variations to be produced by an additional mechanism regulating the formation of stars that is not captured by either Σ
⋆
or Σ
mol
. Studying environmental variations in single galaxies, we find that these variations correlate with changes in the star formation efficiency across environments, which could be linked to the dynamical state of the gas that prevents it from collapsing and forming stars, or to changes in the molecular gas fraction.
NGC 1097 is a nearby Seyfert 1 galaxy with a bright circumnuclear starburst ring, a strong large-scale bar, and an active nucleus. We present a detailed study of the spatial variation of the ...far-infrared (FIR) CII 158 mu m and OI63 mu m lines and mid-infrared H sub(2) emission lines as tracers of gas cooling, and of the polycyclic aromatic hydrocarbon (PAH) bands as tracers of the photoelectric heating, using Herschel-PACS and Spitzer-IRS infrared spectral maps. We focus on the nucleus and the ring, and two star-forming regions (Enuc N and Enuc S). We estimated a photoelectric gas heating efficiency (CII158 mu +OI63 mu m)/PAH in the ring about 50% lower than in Enuc N and S. The average 11.3/7.7 mu m PAH ratio is also lower in the ring, which may suggest a larger fraction of ionized PAHs, but no clear correlation with CII158 mu m/PAH(5.5-14 mu m) is found. PAHs in the ring are responsible for a factor of two more CII158 mu m and OI63 mu m emission per unit mass than PAHs in the Enuc S. spectral energy distribution (SED) modeling indicates that at most 25% of the FIR power in the ring and Enuc S can come from high-intensity photodissociation regions (PDRs), in which case G sub(0) ~ 10 super(2.3) and n sub(H) ~ 10 super(3.5) cm super(-3) in the ring. For these values of G sub(0) and n sub(H), PDR models cannot reproduce the observed H sub(2) emission. Much of the H sub(2) emission in the starburst ring could come from warm regions in the diffuse interstellar medium that are heated by turbulent dissipation or shocks.
Abstract
Molecular gas disks are generally Toomre stable (
Q
T
> 1) and yet clearly gravitationally unstable to structure formation as evidenced by the existence of molecular clouds and ongoing star ...formation. This paper adopts a 3D perspective to obtain a general picture of instabilities in flattened rotating disks, using the 3D dispersion relation to describe how disks evolve when perturbed over their vertical extents. By explicitly adding a vertical perturbation to an unperturbed equilibrium disk, stability is shown to vary with height above the midplane. Near
z
= 0, where the equilibrium density is roughly constant, instability takes on a Jeans-like quality, occurring on scales larger than the Jeans length and subject to a threshold
Q
M
=
κ
2
/(4
π
G
ρ
) = 1 or roughly
Q
T
≈ 2. Far from the midplane, on the other hand, stability is pervasive, and the threshold for the total disk (out to
z
= ±∞) to be stabilized is lowered to
Q
T
= 1 as a consequence. In this new framework, gas disks are able to fragment through partial 3D instability even where total 2D instability is suppressed. The growth rates of the fragments formed via 3D instability are comparable to, or faster than, Toomre instabilities. The rich structure in molecular disks on the scale of tens of parsecs can thus be viewed as a natural consequence of their 3D nature and their exposure to a variety of vertical perturbations acting on roughly a disk scale height, i.e., due to their situation within the more extended galaxy potential, participation in the disk-halo flow, and exposure to star formation feedback.
We present the first public data release (DR1) of the Calar Alto Legacy Integral Field Area (CALIFA) survey. It consists of science-grade optical datacubes for the first 100 of eventually 600 nearby ...galaxies, obtained with the integral-field spectrograph PMAS/PPak mounted on the 3.5 m telescope at the Calar Alto observatory. The galaxies in DR1 already cover a wide range of properties in color-magnitude space, morphological type, stellar mass, and gas ionization conditions. Two different spectral setups are available for each galaxy, (i) a low-resolution V500 setup covering the nominal wavelength range 3745-7500 Angstrom with a spectral resolution of 6.0 Angstrom (FWHM), and (ii) a medium-resolution V1200 setup covering the nominal wavelength range 3650-4840 Angstrom with a spectral resolution of 2.3 Angstrom (FWHM). We present the characteristics and data structure of the CALIFA datasets that should be taken into account for scientific exploitation of the data, in particular the effects of vignetting, bad pixels and spatially correlated noise.
Context.
Star formation and stellar feedback are interlinked processes that redistribute energy, turbulence, and material throughout galaxies. Because young and massive stars form in spatially ...clustered environments, they create pockets of expanding gas termed superbubbles, which retain information about the physical processes that drive them. As these processes play a critical role in shaping galaxy discs and regulating the baryon cycle, measuring the properties of superbubbles provides important input for galaxy evolution models.
Aims.
With the wide coverage and high angular resolution (∼50–150 pc) of the PHANGS–ALMA
12
CO (
J
= 2−1) survey, we can now resolve, identify and characterise a statistically representative number of superbubbles using molecular gas in nearby galaxies.
Methods.
We identify superbubbles by requiring spatial correspondence between shells in CO with stellar populations identified in PHANGS–HST. Then, by combining the properties of the stellar populations with the CO, we quantify the energetics of the stars and constrain feedback models. We visually find 325 cavities across 18 PHANGS–ALMA galaxies, 88 of which have clear superbubble signatures (unbroken shells, central clusters, kinematic signatures of expansion). We measure their radii and expansion velocities using CO (2–1) to dynamically derive their ages and the mechanical power driving the bubbles, which we use to compute the expected properties of the parent stellar populations driving the bubbles.
Results.
We find consistency between the predicted and derived stellar ages and masses of the stellar populations if we use a supernova (SN) model that injects energy with a coupling efficiency of ∼10%. Not only does this confirm that molecular gas accurately traces superbubble properties, but it also provides key observational constraints for superbubble models. We also find evidence that the bubbles are sweeping up gas as they expand, and speculate that these sites have the potential to host new generations of stars.
Conclusions.
This work demonstrates that molecular superbubbles provide novel quantitative constraints on SNe feedback efficiencies and gas clearing times, and represent a promising environment to search for the propagation of star formation, all of which are needed to understand what sets the observed star formation rates in galaxies.
ABSTRACT In a new simple model I reconcile two contradictory views on the factors that determine the rate at which molecular clouds form stars-internal structure versus external, environmental ...influences-providing a unified picture for the regulation of star formation in galaxies. In the presence of external pressure, the pressure gradient set up within a self-gravitating turbulent (isothermal) cloud leads to a non-uniform density distribution. Thus the local environment of a cloud influences its internal structure. In the simple equilibrium model, the fraction of gas at high density in the cloud interior is determined simply by the cloud surface density, which is itself inherited from the pressure in the immediate surroundings. This idea is tested using measurements of the properties of local clouds, which are found to show remarkable agreement with the simple equilibrium model. The model also naturally predicts the star formation relation observed on cloud scales and at the same time provides a mapping between this relation and the closer-to-linear molecular star formation relation measured on larger scales in galaxies. The key is that pressure regulates not only the molecular content of the ISM but also the cloud surface density. I provide a straightforward prescription for the pressure regulation of star formation that can be directly implemented in numerical models. Predictions for the dense gas fraction and star formation efficiency measured on large-scales within galaxies are also presented, establishing the basis for a new picture of star formation regulated by galactic environment.
It has been suggested that gravitational potential can have a significant role in suppressing star formation in nearby galaxies. To establish observational constraints on this scenario, we ...investigated the connection between the dynamics – taking the circular velocity curves (CVCs) as a proxy for the inner gravitational potential – and star formation quenching in 215 non-active galaxies across the Hubble sequence from the Calar Alto Legacy Integral Field Area (CALIFA) survey. Our results show that galaxies with similar CVCs tend to have a certain star-formation quenching pattern. To explore these findings in more details, we constructed kiloparsec(kpc)-resolved relations of the equivalent width of the H
α
(
W
H
α
) versus the amplitude (
V
c
) and shape (
β
= dln
V
c
/dln
R
) of the circular velocity at given radii. We find that the
W
H
α
−
V
c
is a declining relationship, where the retired regions of the galaxies (the ones with
W
H
α
values of below 3 Å) tend to have higher
V
c
. Concurrently,
W
H
α
−
β
is a bimodal relationship, which is characterised by two peaks: concentration of the star forming regions at a positive
β
(rising CVC) and a second concentration of the retired regions with a negative
β
(declining CVC). Our results show that both the amplitude of the CVC – driven by the mass of the galaxies – and its shape – which reflects the internal structure of the galaxies – play an important role in the quenching history of a galaxy.
Abstract Theories of spiral structure traditionally separate into tight-winding Lin–Shu spiral density waves and the swing-amplified material patterns of Goldreich & Lynden-Bell and Julian & Toomre. ...In this paper we consolidate these two types of spirals into a unified description, treating density waves beyond the tight-winding limit, in the regime of shearing and nonsteady open spirals. This shearing wave scenario novelly captures swing amplification that enables structure formation above conventional Q thresholds. However, it also highlights the fundamental role of spiral forcing on the amplification process in general, whether the wave is shearing or not. Thus it captures resonant and nonresonant mode growth through the donkey effect described by Lynden-Bell & Kalnajs and, critically, the cessation of growth when donkey behavior is no longer permitted. Our calculations predict growth exclusive to trailing spirals above the Jeans length, the prominence of spirals across a range of orientations that increases with decreasing arm multiplicity, and a critical orientation where growth is fastest that is the same for both modes and material patterns. Predicted structures are consistent with highly regular, high-multiplicity gaseous spur features and long filaments spaced close to the Jeans scale in spirals and bars. Applied to stellar disks, conditions favor low multiplicity ( m < 5) open trailing spirals with pitch angles in the observed range 10° < i p < 50°. The results of this work serve as a basis for describing spirals as a unified class of transient waves, abundantly stimulated but narrowly selected for growth depending on local conditions.
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