ABSTRACT
By compiling a comprehensive census of literature studies, we investigate the evolution of the main sequence (MS) of star-forming galaxies (SFGs) in the widest range of redshift (0 < z < 6) ...and stellar mass (108.5–1011.5 M⊙) ever probed. We convert all observations to a common calibration and find a remarkable consensus on the variation of the MS shape and normalization across cosmic time. The relation exhibits a curvature towards the high stellar masses at all redshifts. The best functional form is governed by two parameters: the evolution of the normalization and the turnover mass (M0(t)), which both evolve as a power law of the Universe age. The turn-over mass determines the MS shape. It marginally evolves with time, making the MS slightly steeper towards z ∼ 4–6. At stellar masses below M0(t), SFGs have a constant specific SFR (sSFR), while above M0(t) the sSFR is suppressed. We find that the MS is dominated by central galaxies. This allows to turn M0(t) into the corresponding host halo mass. This evolves as the halo mass threshold between cold and hot accretion regimes, as predicted by the theory of accretion, where the central galaxy is fed or starved of cold gas supply, respectively. We, thus, argue that the progressive MS bending as a function of the Universe age is caused by the lower availability of cold gas in haloes entering the hot accretion phase, in addition to black hole feedback. We also find qualitatively the same trend in the largest sample of star-forming galaxies provided by the IllustrisTNG simulation. Nevertheless, we still note large quantitative discrepancies with respect to observations, in particular at the high-mass end. These can not be easily ascribed to biases or systematics in the observed SFRs and the derived MS.
We present a comprehensive study of the Na I λ5890, 5895 (Na I D) resonant lines in the Sloan Digital Sky Survey (SDSS, DR7) spectroscopic sample to look for neutral gas outflows in the local ...galaxies. Individual galaxy spectra are stacked in bins of stellar mass (M⋆) and star formation rate (SFR) to investigate the dependence of galactic wind occurrence and velocity as a function of the galaxy position in the SFR-M⋆ plane. While in most cases the interstellar medium (ISM) absorption and emission lines are at the galaxy systemic velocity, in massive galaxies (M⋆ > 5 × M⊙) at the high SFR tail (SFR > 10−12 M⊙ yr−1) we find evidence of a significant blue-shifted Na I D absorption, which we interpret as evidence of neutral outflowing gas. The occurrence of the blue-shifted absorption in the stacked spectra does not depend on the contribution of the nuclear activity as it is observed at the same significance for purely star-forming (SF) galaxies, active galactic nuclei (AGN), and composite systems at fixed SFR. We confirm, instead, for all classes of objects a clear dependence on the galaxy disc inclination: the blueshift is the largest and the Na I D equivalent width the smallest for face-on galaxies, while the absorption feature is at the systemic velocity for edge-on systems. This indicates that the neutral outflow is mostly perpendicular or biconical with respect to the galactic disc. We also compare the kinematics of the neutral gas with the ionized gas phase as traced by the OIIIλ5007, Hα, NIIλ6548, and NIIλ6584 emission lines in the same galaxy spectra. Differently for the neutral gas phase, all the emission lines show evidence of perturbed kinematics only in galaxies with a significant level of nuclear activity, and they are independent of the galactic disc inclination. This would suggest that, while neutral winds originate from the galactic disc and are powered by SF feedback, ionized outflows are instead due to AGN feedback originating from the black hole accretion disc. In both the neutral and ionized gas phases, the observed wind velocities (of the order of 100−200 kms−1) suggest that the outflowing gas remains bound to the galaxy with no definitive effect on the gas reservoir.
By using a set of different star formation rate (SFR) indicators, including Wide-field Infrared Survey Explorer (WISE) mid-infrared and H α emission, we study the slope of the main sequence (MS) of ...local star-forming galaxies at stellar masses larger than 10^{10} M_{⊙ }. The slope of the relation strongly depends on the SFR indicator used. In all cases, the local MS shows a bending at high stellar masses with respect to the slope obtained in the low-mass regime. While the distribution of galaxies in the upper envelope of the MS is consistent with a lognormal distribution, the lower envelope shows an excess of galaxies, which increases as a function of the stellar mass but varies as a function of the SFR indicator used. The scatter of the best lognormal distribution increases with stellar mass from ∼0.3 dex at 10^{10} M_{⊙ } to ∼0.45 at 10^{11} M_{⊙ }. The MS high-mass end is dominated by central galaxies of group-sized haloes with a red bulge and a disc redder than the lower mass counterparts. We argue that the MS bending in this region is due to two processes: (i) the formation of a bulge component as a consequence of the increased merger activity in groups, and (ii) the cold gas starvation induced by the hot halo environment, which cuts off the gas inflow on to the disc. Similarly, the increase of the MS scatter at high stellar masses would be explained by the larger spread of star formation histories of central group and cluster galaxies with respect to lower mass systems.
We use a sample built on the SDSS DR7 catalogue and the bulge-disc decomposition of Simard et al. (2011, ApJS, 196, 11) to study how the bulge and disc components contribute to the parent galaxy’s ...star formation activity, by determining its position in the star formation rate (SFR) – stellar mass (M⋆) plane at 0.02 < z < 0.1 and around the main sequence (MS) of star-forming galaxies. For this purpose, we use the bulge and disc colours as proxy for their SFRs, while the total galaxy SFR comes from Hα or D4000. We study the mean galaxy bulge-total mass ratio (B/T) as a function of the residual from the MS (ΔMS) and find that the B/T-ΔMS relation exhibits a parabola-like shape with the peak of the MS corresponding to the lowest B/Ts at any stellar mass. The lower and upper envelope of the MS are populated by galaxies with similar B/T, velocity dispersion and concentration (R90/R50) values. The mean values of such distributions indicate that the majority of the galaxies are characterised by classical bulges and not pseudo-bulges. Bulges above the MS are characterised by blue colours or, when red, by a high level of dust obscuration, thus indicating that in both cases they are actively star forming. When on the MS or below it, bulges are mostly red and dead. At stellar masses above 1010.5M⊙, bulges on the MS or in the green valley tend to be significantly redder than their counterparts in the quiescence region, despite similar levels of dust obscuration. This could be explained with different age or metallicity content, suggesting different evolutionary paths for bulges on the MS and green valley with respect to those in the quiescence region. The disc g−r colour anti-correlates at any mass with the distance from the MS, getting redder when approaching the MS lower envelope and the quiescence region. The anti-correlation flattens as a function of the stellar mass, likely due to a higher level of dust obscuration in massive SF galaxies. We conclude that the position of a galaxy in the Log SFR – Log M⋆ plane depends on the star formation activity of its components: above the MS both bulge and disc are actively star forming. The nuclear activity is the first to be suppressed, moving the galaxies on the MS. Once the disc stops forming stars as well, the galaxy moves below the MS and eventually to the quiescence region. This is confirmed by a significant percentage (~45%) of passive galaxies with a secure two component morphology, coexisting with a population of pure spheroidals. Our findings are qualitatively in agreement with the compaction-depletion scenario, in which subsequent phases of gas inflow in the centre of a galaxy and depletion due to high star formation activity move the galaxy across the MS before the final quenching episode takes place.
ABSTRACT
By using the deepest available mid- and far-infrared surveys in the CANDELS, GOODS, and COSMOS fields we study the evolution of the main sequence (MS) of star-forming galaxies (SFGs) from z ...∼ 0 to ∼ 2.5 at stellar masses larger than 1010 M⊙. The MS slope and scatter are consistent with a rescaled version of the local relation and distribution, shifted at higher values of star formation rate (SFR) according to ∝ (1 + $z$)3.2. The relation exhibits a bending at the high-mass end and a slightly increasing scatter as a function of the stellar mass. We show that the previously reported evolution of the MS slope, in the considered mass and redshift range, is due to a selection effect. The distribution of galaxies in the MS region at fixed stellar mass is well represented by a single lognormal distribution at all redshifts and masses, with starburst galaxies occupying the tail at high SFR.
ABSTRACT
We use the first release of the SDSS/MaStar stellar library comprising ∼9000, high S/N spectra, to calculate integrated spectra of stellar population models. The models extend over the ...wavelength range 0.36–1.03 µm and share the same spectral resolution ($R\sim 1800$) and flux calibration as the SDSS-IV/MaNGA galaxy data. The parameter space covered by the stellar spectra collected thus far allows the calculation of models with ages and chemical composition in the range $\rm {\mathit{ t}\gt 200 \,Myr, -2 \lt = Z/H \lt = + 0.35}$, which will be extended as MaStar proceeds. Notably, the models include spectra for dwarf main-sequence stars close to the core H-burning limit, as well as spectra for cold, metal-rich giants. Both stellar types are crucial for modelling λ > 0.7 µm absorption spectra. Moreover, a better parameter coverage at low metallicity allows the calculation of models as young as 500 Myr and the full account of the blue horizontal branch phase of old populations. We present models adopting two independent sets of stellar parameters (Teff, log g, Z/H). In a novel approach, their reliability is tested ‘on the fly’ using the stellar population models themselves. We perform tests with Milky Way and Magellanic Clouds globular clusters, finding that the new models recover their ages and metallicities remarkably well, with systematics as low as a few per cent for homogeneous calibration sets. We also fit a MaNGA galaxy spectrum, finding residuals of the order of a few per cent comparable to the state-of-art models, but now over a wider wavelength range.
Near-infrared spectroscopy (NIRS) signals quantify the oxygenated (Δ
) and deoxygenated (Δ
) heme group concentrations. Δ
has been preferred to Δ
in evaluating skeletal muscle oxygen extraction ...because it is assumed to be less sensitive to blood volume (BV) changes, but uncertainties exist on this assumption. To analyze this assumption, a computational model of oxygen transport and metabolism is used to quantify the effect of O
delivery and BV changes on the NIRS signals from a canine model of muscle oxidative metabolism (Sun Y, Ferguson BS, Rogatzki MJ, McDonald JR, Gladden LB.
48: 2013-2020, 2016). The computational analysis accounts for microvascular (Δ
, Δ
) and extravascular (Δ
, Δ
) oxygenated and deoxygenated forms. Simulations predicted muscle oxygen uptake and NIRS signal changes well for blood flows ranging from resting to contracting muscle. Additional NIRS signal simulations were obtained in the absence or presence of BV changes corresponding to a heme groups concentration changes (Δ
= 0-48 µM). Under normal delivery (
= 1.0 L·kg
·min
) in contracting muscle, capillary oxygen saturation (So
) was 62% with capillary Δ
and Δ
of ± 41 µΜ for ΔHbMb = 0. An increase of BV (Δ
= 24 µΜ) caused a Δ
decrease (16µΜ) almost twice as much as the increase observed for Δ
(9 µΜ). When So
increased to more than 80%, only Δ
was significantly affected by BV changes. The analysis indicates that microvascular So
is a key factor in determining the sensitivity of Δ
and deoxygenated Δ
to BV changes. Contrary to a common assumption, the Δ
is affected by BV changes in normal contracting muscle and even more in the presence of impaired O
delivery.
Deoxygenated is preferred to the oxygenated near-infrared spectroscopy signal in evaluating skeletal muscle oxygen extraction because it is assumed to be insensitive to blood volume changes. The quantitative analysis proposed in this study indicates that even in absence of skin blood flow effects, both NIRS signals in presence of either normal or reduced oxygen delivery are affected by blood volume changes. These changes should be considered to properly quantify muscle oxygen extraction by NIRS methods.
Light breeze in the local Universe Concas, A.; Popesso, P.; Brusa, M. ...
Astronomy and astrophysics (Berlin),
10/2017, Letnik:
606
Journal Article
Recenzirano
Odprti dostop
We analyze a complete spectroscopic sample of galaxies (~600 000) drawn from Sloan Digital Sky Survey (SDSS, DR7) to look for evidence of galactic winds in the local Universe. We focus on the shape ...of the OIIIλ5007 emission line as a tracer of ionizing gas outflows. We stack our spectra in a fine grid of star formation rate (SFR) and stellar mass to analyze the dependence of winds on the position of galaxies in the SFR versus mass diagram. We do not find any significant evidence of broad and shifted OIIIλ5007 emission line which we interpret as no evidence of outflowing ionized gas in the global population. We have also classified these galaxies as star-forming or AGN-dominated according to their position in the standard BPT diagram. We show how the average OIIIλ5007 profile changes as a function of the nature of the dominant ionizing source. We find that in the star-forming dominated source the oxygen line is symmetric and governed by the gravitational potential well. The AGN or composite AGN\star-formation activity objects, in contrast, display a prominent and asymmetric profile that can be well described by a broad Gaussian component that is blue-shifted from a narrow symmetric core. In particular, we find that the blue wings of the average OIIIλ5007 profiles are increasingly prominent in the LINERs and Seyfert galaxies. We conclude that, through the identification of strong bulk motion as traced by the warm ionized gas, in the low-redshift Universe, “pure” star-formation activity does not seem capable of driving ionized-gas outflows, while, the presence of optically selected AGN seems to play a primary role. We discuss the implications of these results for the role of the quenching mechanism in the present-day Universe.
ABSTRACT
We use dust masses (Mdust) derived from far-infrared data and molecular gas masses (Mmol) based on CO luminosity to calibrate proxies based on a combination of the galaxy Balmer decrement, ...disc inclination, and gas metallicity. We use such proxies to estimate Mdust and Mmol in the local SDSS sample of star-forming galaxies (SFGs). We study the distribution of Mdust and Mmol along and across the main sequence (MS) of SFGs. We find that Mdust and Mmol increase rapidly along the MS with increasing stellar mass (M*), and more marginally across the MS with increasing SFR (or distance from the relation). The dependence on M* is sub-linear for both Mdust and Mmol. Thus, the fraction of dust (fdust) and molecular gas mass (fmol) decreases monotonically towards large M*. The star formation efficiency (SFE, inverse of the molecular gas depletion time) depends strongly on the distance from the MS and it is constant along the MS. As nearly all galaxies in the sample are central galaxies, we estimate the dependence of fdust and fgas on the host halo mass and find a tight anticorrelation. As the region where the MS is bending is numerically dominated by massive haloes, we conclude that the bending of the MS is due to a lower availability of molecular gas mass in massive haloes rather than a lower efficiency in forming stars.
The utilization of continuous wave (CW) near-infrared spectroscopy (NIRS) device to measure non-invasively muscle oxygenation in healthy and disease states is limited by the uncertainties related to ...the differential path length factor (DPF). DPF value is required to quantify oxygenated and deoxygenated heme groups’ concentration changes from measurement of optical densities by NIRS. An integrated approach that combines animal and computational models of oxygen transport and utilization was used to estimate the DPF value in situ. The canine model of muscle oxidative metabolism allowed measurement of both venous oxygen content and tissue oxygenation by CW NIRS under different oxygen delivery conditions. The experimental data obtained from the animal model were integrated in a computational model of O2 transport and utilization and combined with Beer-Lambert law to estimate DPF value in contracting skeletal muscle. A 2.1 value was found for DPF by fitting the mathematical model to the experimental data obtained in contracting muscle (T3) (Med.Sci.Sports.Exerc.48(10):2013–2020,2016). With the estimated value of DPF, model simulations well predicted the optical density measured by NIRS on the same animal model but with different blood flow, arterial oxygen contents and contraction rate (J.Appl.Physiol.108:1169–1176, 2010 and 112:9–19,2013) and demonstrated the robustness of the approach proposed in estimating DPF value. The approach used can overcome the semi-quantitative nature of the NIRS and estimate non-invasively DPF to obtain an accurate concentration change of oxygenated and deoxygenated hemo groups by CW NIRS measurements in contracting skeletal muscle under different oxygen delivery and contraction rate.
•The measurement of hemo groups concentration change (ΔHbMbO2, ΔHHbMb) by continuous wave CW-NIRS devices relies on the differential path length factor (DPF) value.•The DPF value varies with experimental condition and is unclear how contraction affects the concentration change by CW-NIRS.•The integrated approach proposed overcomes the NIRS signal nature and allows us to estimate the DPF value in contracting muscle.•The estimated DPF value can be used in CW-NIRS devices to quantify the oxygenation (ΔHbMbO2, ΔHHbMb) in contracting muscle.•With this approach CW-NIRS devices can quantify muscle oxygenation under different oxygen delivery and perfusion conditions.
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