We investigated the mass-to-light vs. color relations (MLCRs) derived from the spatially resolved star formation history of a sample of 452 galaxies observed with integral field spectroscopy in the ...CALIFA survey. We derived the stellar mass (
M
⋆
) and the stellar mass surface density (Σ
⋆
) from the combination of full spectral fitting (using different sets of stellar population models) with observed and synthetic colors in optical broad bands. This method allows obtaining the radial structure of the mass-to-light ratio (
M
/
L
) at several wavelengths and studying the spatially resolved MLCRs. Our sample covers a wide range of Hubble types from Sc to E, with stellar masses ranging from
M
⋆
∼ 10
8.4
to 10
12
M
⊙
. The scatter in the MLCRs was studied as a function of morphology, stellar extinction, and emission line contribution to the colors. The effects of the initial mass function (IMF) and stellar population models in the MLCRs were also explored. Our main results are that
(a)
the
M
/
L
ratio has a negative radial gradient that is steeper within the central 1 half-light-radius (HLR). It is steeper in Sb-Sbc than in early-type galaxies.
(b)
The MLCRs between
M
/
L
and optical colors were derived with a scatter of ∼0.1 dex. The smallest dispersion was found for the combinations (
i
,
g
−
r
) and (
R
,
B
−
R
). Extinction and emission line contributions do not affect the scatter of these relations. Morphology does not produce a significant effect, except if the general relation is used for galaxies redder than (
u
−
i
) > 4 or bluer than (
u
−
i
)< 0.
(c)
The IMF has a large effect on MLCRs, as expected. The change from a Chabrier to a Salpeter IMF produces a median shift of ∼0.29 dex when mass loss from stellar evolution is also taken into account.
(d)
These MLCRs are in agreement with previous results, in particular for relations with
g
and
r
bands and the
B
and
V
Johnson systems.
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We report on a detailed study of the stellar populations and ionized gas properties in the merger LIRG NGC 2623, analyzing optical integral field spectroscopy from the CALIFA survey and PMAS LArr, ...multiwavelength HST imaging, and OSIRIS narrow band Hα and NIIλ6584 imaging. The spectra were processed with the starlight full spectral fitting code, and the results are compared with those for two early-stage merger LIRGs (IC 1623 W and NGC 6090), together with CALIFA Sbc/Sc galaxies. We find that NGC 2623 went through two periods of increased star formation (SF), a first and widespread episode, traced by intermediate-age stellar populations ISP (140 Myr–1.4 Gyr), and a second one, traced by young stellar populations YSP (<140 Myr), which is concentrated in the central regions (<1.4 kpc). Our results are in agreement with the epochs of the first peri-center passage (~200 Myr ago) and coalescence (<100 Myr ago) predicted by dynamical models, and with high-resolution merger simulations in the literature, consistent with NGC 2623 representing an evolved version of the early-stage mergers. Most ionized gas is concentrated within <2.8 kpc, where LINER-like ionization and high-velocity dispersion (~220 km s-1) are found, consistent with the previously reported outflow. As revealed by the highest-resolution OSIRIS and HST data, a collection of HII regions is also present in the plane of the galaxy, which explains the mixture of ionization mechanisms in this system. It is unlikely that the outflow in NGC 2623 will escape from the galaxy, given the low SFR intensity (~0.5 M⊙ yr-1 kpc-2), the fact that the outflow rate is three times lower than the current SFR, and the escape velocity in the central areas is higher than the outflow velocity.
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This paper presents the spatially resolved star formation history (SFH) of nearby galaxies with the aim of furthering our understanding of the different processes involved in the formation and ...evolution of galaxies. To this end, we apply the fossil record method of stellar population synthesis to a rich and diverse data set of 436 galaxies observed with integral field spectroscopy in the CALIFA survey. The sample covers a wide range of Hubble types, with stellar masses ranging from
M
⋆
~ 10
9
to 7 × 10
11
M
⊙
. Spectral synthesis techniques are applied to the datacubes to retrieve the spatially resolved time evolution of the star formation rate (SFR), its intensity (Σ
SFR
), and other descriptors of the 2D SFH in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd) and five bins of stellar mass. Our main results are that (a) galaxies form very fast independently of their current stellar mass, with the peak of star formation at high redshift (
z
> 2). Subsequent star formation is driven by
M
⋆
and morphology, with less massive and later type spirals showing more prolonged periods of star formation. (b) At any epoch in the past, the SFR is proportional to
M
⋆
, with most massive galaxies having the highest absolute (but lowest specific) SFRs. (c) While today, the Σ
SFR
is similar for all spirals and significantly lower in early-type galaxies (ETG), in the past, the Σ
SFR
scales well with morphology. The central regions of today’s ETGs are where the Σ
SFR
reached the highest values (> 10
3
M
⊙
Gyr
-1
pc
-2
), similar to those measured in high-redshift star-forming galaxies. (d) The evolution of Σ
SFR
in Sbc systems matches that of models for Milky Way-like galaxies, suggesting that the formation of a thick disk may be a common phase in spirals at early epochs. (e) The SFR and Σ
SFR
in outer regions of E and S0 galaxies show that they have undergone an extended phase of growth in mass between
z
= 2 and 0.4. The mass assembled in this phase is in agreement with the two-phase scenario proposed for the formation of ETGs. (f) Evidence of an early and fast quenching is found only in the most massive (
M
⋆
> 2 × 10
11
M
⊙
) E galaxies of the sample, but not in spirals of similar mass, suggesting that halo quenching is not the main mechanism for the shut down of star formation in galaxies. Less massive E and disk galaxies show more extended SFHs and a slow quenching. (g) Evidence of fast quenching is also found in the nuclei of ETG and early spirals, with SFR and Σ
SFR
indicating that they can be the relic of the “red nuggets” detected at high redshift.
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The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) is expected to map thousands of square degrees of the northern sky with 56 narrowband filters (spectral resolution of
...R
∼ 60) in the upcoming years. This resolution allows us to study emission line galaxies (ELGs) with a minimum equivalent width of 10 Å in the H
α
emission line for a median signal-to-noise ratio (S/N) of 5. This will make J-PAS a very competitive and unbiased emission line survey compared to spectroscopic or narrowband surveys with fewer filters. The miniJPAS survey covered 1 deg
2
, and it used the same photometric system as J-PAS, but the observations were carried out with the pathfinder J-PAS camera. In this work, we identify and characterize the sample of ELGs from miniJPAS with a redshift lower than 0.35, which is the limit to which the H
α
line can be observed with the J-PAS filter system. Using a method based on artificial neural networks, we detect the ELG population and measure the equivalent width and flux of the H
α
, H
β
, O
III
, and N
II
emission lines. We explore the ionization mechanism using the diagrams OIII/H
β
versus NII/H
α
(BPT) and EW(H
α
) versus NII/H
α
(WHAN). We identify 1787 ELGs (83%) from the parent sample (2154 galaxies) in the AEGIS field. For the galaxies with reliable EW values that can be placed in the WHAN diagram (2000 galaxies in total), we obtained that 72.8 ± 0.4%, 17.7 ± 0.4%, and 9.4 ± 0.2% are star-forming (SF), active galactic nucleus (Seyfert), and quiescent galaxies, respectively. The distribution of EW(H
α
) is well correlated with the bimodal color distribution of galaxies. Based on the rest-frame (
u
−
r
)–stellar mass diagram, 94% of the blue galaxies are SF galaxies, and 97% of the red galaxies are LINERs or passive galaxies. The nebular extinction and star formation rate (SFR) were computed from the H
α
and H
β
fluxes. We find that the star formation main sequence is described as log SFR
M
⊙
yr
−1
= 0.90
−0.02
+0.02
log
M
⋆
M
⊙
−8.85
−0.20
+0.19
and has an intrinsic scatter of 0.20
−0.01
+0.01
. The cosmic evolution of the SFR density (
ρ
SFR
) is derived at three redshift bins: 0 <
z
≤ 0.15, 0.15 <
z
≤ 0.25, and 0.25 <
z
≤ 0.35, which agrees with previous results that were based on measurements of the H
α
emission line. However, we find an offset with respect to other estimates that were based on the star formation history obtained from fitting the spectral energy distribution of the stellar continuum. We discuss the origin of this discrepancy, which is probably a combination of several factors: the escape of ionizing photons, the SFR tracers, and dust attenuation, among others.
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We studied the global and local M-Z relation based on the first data available from the CALIFA survey (150 galaxies). This survey provides integral field spectroscopy of the complete optical extent ...of each galaxy, with a resolution high enough to separate individual HIT regions and/or aggregations. About 3000 individual HIT regions have been detected. The spectra cover the wavelength range between 0113727 and SIT 6731, with a sufficient signal-to-noise ratio to derive the oxygen abundance and star-formation rate associated with each region. In addition, we computed the integrated and spatially resolved stellar masses based on SDSS photometric data. We explore the relations between the stellar mass, oxygen abundance and star-formation rate using this dataset. Our results agree with the scenario in which gas recycling in galaxies, both locally and globally, is much faster than other typical timescales, such like that of gas accretion by inflow and/or metal loss due to outflows. In essence, late-type/disk-dominated galaxies seem to be in a quasi-steady situation, with a behavior similar to the one expected from an instantaneous recycling/closed-box model.
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ABSTRACT Extremely metal-poor (XMP) galaxies are defined to have a gas-phase metallicity smaller than a tenth of the solar value ( ). They are uncommon, chemically and possibly dynamically primitive, ...with physical conditions characteristic of earlier phases of the universe. We search for new XMPs in the Sloan Digital Sky Survey (SDSS) in a work that complements Paper I. This time, high electron temperature objects are selected; metals are a main coolant of the gas, so metal-poor objects contain high-temperature gas. Using the algorithm k-means, we classify 788,677 spectra to select 1281 galaxies that have particularly intense O iiiλ4363 with respect to O iiiλ5007, which is a proxy for high electron temperature. The metallicity of these candidates was computed using a hybrid technique consistent with the direct method, rendering 196 XMPs. A less restrictive noise constraint provides a larger set with 332 candidates. Both lists are provided in electronic format. The selected XMP sample has a mean stellar mass around , with the dust mass for typical star-forming regions. In agreement with previous findings, XMPs show a tendency to be tadpole-like or cometary. Their underlying stellar continuum corresponds to a fairly young stellar population ( ), although young and aged stellar populations coexist at the low-metallicity starbursts. About 10% of the XMPs show large N/O. Based on their location in constrained cosmological numerical simulations, XMPs have a strong tendency to appear in voids and to avoid galaxy clusters. The puzzling 2%-solar low-metallicity threshold exhibited by XMPs remains.
Context. The star formation rate (SFR) is one of the main parameters used to analyze the evolution of galaxies through time. The need for recovering the light reprocessed by dust commonly requires ...the use of low spatial resolution far-infrared data. Recombination line luminosities provide an alternative, although uncertain dust-extinction corrections based on narrowband imaging or long-slit spectroscopy have traditionally posed a limit to their applicability. Integral field spectroscopy (IFS) is clearly the way to overcome this kind of limitation. Aims. We obtain integrated Hα, ultraviolet (UV) and infrared (IR)-based SFR measurements for 272 galaxies from the CALIFA survey at 0.005 <z< 0.03 using single-band and hybrid tracers. We aim to determine whether the extinction-corrected Hα luminosities provide a good measure of the SFR and to shed light on the origin of the discrepancies between tracers. Updated calibrations referred to Hα are provided. The well-defined selection criteria and large statistics allow us to carry out this analysis globally and split by properties, including stellar mass and morphological type. Methods. We derive integrated, extinction-corrected Hα fluxes from CALIFA, UV surface and asymptotic photometry from GALEX and integrated WISE 22 μm and IRAS fluxes. Results. We find that the extinction-corrected Hα luminosity agrees with the hybrid updated SFR estimators based on either UV or Hα plus IR luminosity over the full range of SFRs (0.03−20 M⊙ yr-1). The coefficient that weights the amount of energy produced by newly-born stars that is reprocessed by dust on the hybrid tracers, aIR, shows a large dispersion. However, this coefficient does not became increasingly small at high attenuations, as expected if significant highly-obscured Hα emission were missed, i.e., after a Balmer decrement-based attenuation correction is applied. Lenticulars, early-type spirals, and type-2 AGN host galaxies show smaller coefficients because of the contribution of optical photons and AGN to dust heating. Conclusions. In the local Universe, the Hα luminosity derived from IFS observations can be used to measure SFR, at least in statistically-significant, optically-selected galaxy samples, once stellar continuum absorption and dust attenuation effects are accounted for. The analysis of the SFR calibrations by galaxies properties could potentially be used by other works to study the impact of different selection criteria in the SFR values derived, and to disentangle selection effects from other physically motivated differences, such as environmental or evolutionary effects.
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The search of extragalactic regions with conspicuous presence of Wolf-Rayet (WR) stars outside the Local Group is challenging task owing to the difficulty in detecting their faint spectral features. ...In this exploratory work, we develop a methodology to perform an automated search of WR signatures through a pixel-by-pixel analysis of integral field spectroscopy (IFS) data belonging to the Calar Alto Legacy Integral Field Area survey, CALIFA. This procedure has been applied to a sample of nearby galaxies spanning a wide range of physical, morphological, and environmental properties. This technique allowed us to build the first catalogue of regions rich in WR stars with spatially resolved information, and enabled us to study the properties of these complexes in a two-dimensional (2D) context. The detection technique is based on the identification of the blue WR bump (around He iiλ4686 Å, mainly associated with nitrogen-rich WR stars; WN) and the red WR bump (around C ivλ5808 Å, mainly associated with carbon-rich WR stars; WC) using a pixel-by-pixel analysis that maximizes the number of independent regions within a given galaxy. We identified 44 WR-rich regions with blue bumps distributed in 25 out of a total of 558 galaxies. The red WR bump was identified only in 5 of those regions. Most of the WR regions are located within one effective radius from the galaxy centre, and around one-third are located within ~1 kpc or less from the centre. We found that the majority of the galaxies hosting WR populations in our sample are involved in some kind of interaction process. Half of the host galaxies share some properties with gamma-ray burst (GRB) hosts where WR stars, such as potential candidates to the progenitors of GRBs, are found. We also compared the WR properties derived from the CALIFA data with stellar population synthesis models, and confirm that simple star models are generally not able to reproduce the observations. We conclude that other effects, such as binary star channel (which could extend theWR phase up to 10 Myr), fast rotation, or other physical processes that cause the loss of observed Lyman continuum photons, very likely affect the derived WR properties, and hence should be considered when modelling the evolution of massive stars.
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