اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدOn the metallicity dependence of the 24micron luminosity as a star formation tracer
142
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We investigate the use of the rest-frame 24microns luminosity as an indicator of the star formation rate (SFR) in galaxies with different metallicities by comparing it to the (extinction corrected) Halpha luminosity. We carry out this analysis in 2 steps: First, we compare the emission from HII regions in different galaxies with metallicities between 12+log(O/H) = 8.1 and 8.9. We find that the 24microns and the extinction corrected Halpha luminosities from individual HII regions follow the same correlation for all galaxies, independent of their metallicity. Second, the role of metallicity is explored further for the integrated luminosity in a sample of galaxies with metallicities in the range of 12+log(O/H) = 7.2 - 9.1. For this sample we compare the 24microns and Halpha luminosities integrated over the entire galaxies and find a lack of the 24microns emission for a given Halpha luminosity for low metallicity objects, likely reflecting a low dust content. These results suggest that the 24microns luminosity is a good metallicity independent tracer for the SFR in individual HII regions. On the other hand, metallicity has to be taken into account when using the 24microns luminosity as a tracer for the SFR of entire galaxies.
قيم البحث
اقرأ أيضاً
IR emission bands at 3.3, 6.2, 7.7, 8.6 and 11.3 um are generally attributed to IR fluorescence from (mainly) FUV pumped PAHs. As such, they trace the FUV stellar flux and are a measure of star formation. We examined the IR spectral characteristics o
f Galactic star forming regions, normal and starburst galaxies, AGNs and ULIRGs. The goal is to analyze if PAH bands are a good qualitative and/or quantitative tracer of star formation and hence the application of PAH bands as a diagnostic in order to identify the dominant processes contributing to the IR emission from Seyferts and ULIRGs. We develop a MIR/FIR diagnostic and compare it to known diagnostics, with these also applied to the Galactic sample. This diagnostic is based on the FIR normalized 6.2 um PAH flux and the FIR normalized 6.2 um continuum flux. The Galactic sources form a sequence spanning a range of 3 orders of magnitude, from embedded compact HII regions to exposed PDRs and the (D)ISM. The variation in the 6.2 um PAH/continuum ratio is relative small. Normal and starburst galaxies ressemble exposed PDRs. While Seyfert-2s coincide with the starburst trend, Seyfert-1s are displaced by at least a factor 10 in 6.2 um continuum flux. ULIRGs show a diverse spectral appearance (AGN hot dust continuum, starburst-like or strong dust obscuration in the nucleus). ULIRGs also seems to have more prominent FIR emission than either starburst galaxies or AGNs. We discuss the observed variation in the Galactic sample in view of the evolutionary state and the PAH/dust abundance and the use of PAHs as quantitative tracers of star formation activity. We find that PAHs may be better suited as a tracer of B stars, which dominate the Galactic stellar energy budget, than as a tracer of massive star formation (O stars).
We investigate if dust emission in the far-IR continuum provides a robust estimate of star formation rate (SFR) for a nearby, normal late-type galaxy. We focus on the ratio of the 40--1000 micron luminosity (L_dust) to the far-UV (0.165 micron lumino
sity, which is connected to recent episodes of star formation. Available total photometry at 0.165, 60, 100 and 170 micron limits the statistics to 30 galaxies, which, however, span a large range in observed (and, thus, attenuated by dust) K-band (2.2 micron) luminosity, morphology and inclination (i). This sample shows that the ratio of L_dust to the observed far-UV luminosity depends not only on i, as expected, but also on morphology and, in a tighter way, on observed K-band luminosity. We find that L_dust/L_FUV is proportional to e^(-tau_K) (alpha+0.62) (L_K)^(0.62), where L_FUV and L_K are the unattenuated stellar luminosities in far-UV and K, respectively, and alpha is the ratio of the attenuation optical depths at 0.165 micron (tau_FUV) and 2.2 micron (tau_K). This relation is to zeroth order independent of i and morphology. It may be further expressed as L_dust/L_FUV proportional to (L_K)^delta, where delta = 0.61 - 0.02 alpha, under the observationally-motivated assumption that, for an average inclination, e^(-tau_K) is proportional to (L_K)^(-0.02). We adopt calculations of two different models of attenuation of stellar light by internal dust to derive solid-angle averaged values of alpha. We find that delta is positive and decreases towards 0 from the more luminous to the less luminous galaxies. This means that there is no universal ratio of far-IR luminosity to unattenuated far-UV luminosity for nearby, normal late-type galaxies. (Abridged)
The [CII] 157.74 $mu$m transition is the dominant coolant of the neutral interstellar gas, and has great potential as a star formation rate (SFR) tracer. Using the Herschel KINGFISH sample of 46 nearby galaxies, we investigate the relation of [CII] s
urface brightness and luminosity with SFR. We conclude that [CII] can be used for measurements of SFR on both global and kiloparsec scales in normal star-forming galaxies in the absence of strong active galactic nuclei (AGN). The uncertainty of the $Sigma_{rm [CII]}-Sigma_{rm SFR}$ calibration is $pm$0.21 dex. The main source of scatter in the correlation is associated with regions that exhibit warm IR colors, and we provide an adjustment based on IR color that reduces the scatter. We show that the color-adjusted $Sigma_{rm[CII]}-Sigma_{rm SFR}$ correlation is valid over almost 5 orders of magnitude in $Sigma_{rm SFR}$, holding for both normal star-forming galaxies and non-AGN luminous infrared galaxies. Using [CII] luminosity instead of surface brightness to estimate SFR suffers from worse systematics, frequently underpredicting SFR in luminous infrared galaxies even after IR color adjustment (although this depends on the SFR measure employed). We suspect that surface brightness relations are better behaved than the luminosity relations because the former are more closely related to the local far-UV field strength, most likely the main parameter controlling the efficiency of the conversion of far-UV radiation into gas heating. A simple model based on Starburst99 population-synthesis code to connect SFR to [CII] finds that heating efficiencies are $1%-3%$ in normal galaxies.
We have assessed the influence of the stellar iron content on the Cepheid Period-Luminosity (PL) relation by relating the V band residuals from the Freedman et al (2001) PL relation to [Fe/H] for 68 Galactic and Magellanic Cloud Cepheids. The iron ab
undances were measured from FEROS and UVES high-resolution and high signal-to-noise optical spectra. Our data indicate that the stars become fainter as metallicity increases, until a plateau or turnover point is reached at about solar metallicity. This behavior appears at odds both with the PL relation being independent from iron abundance and with Cepheids becoming monotonically brighter as metallicity increases (e.g. Kennicutt et al 1998, Sakai et al 2004).
We present the results on the study of 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 (up to 2-
3 effective radii), with enough resolution to separate individual HII regions and/or aggregations. Nearly $sim$3000 individual HII regions have been detected. The spectra cover the wavelength range between [OII]3727 and [SII]6731, with a sufficient signal-to-noise to derive the oxygen abundance and star-formation rate associated with each region. In addition, we have computed the integrated and spatially resolved stellar masses (and surface densities), based on SDSS photometric data. We explore the relations between the stellar mass, oxygen abundance and star-formation rate using this dataset. We derive a tight relation between the integrated stellar mass and the gas-phase abundance, with a dispersion smaller than the one already reported in the literature ($sigma_{Delta{rm log(O/H)}}=$0.07 dex). Indeed, this dispersion is only slightly larger than the typical error derived for our oxygen abundances. However, we do not find any secondary relation with the star-formation rate, other than the one induced due to the primary relation of this quantity with the stellar mass. We confirm the result using the $sim$3000 individual HII regions, for the corresponding local relations. Our results agree with the scenario in which gas recycling in galaxies, both locally and globally, is much faster than other typical timescales, 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.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
