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Register a new userThe halo mass function of late-type galaxies from HI kinematics
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We present an empirical method to measure the halo mass function (HMF) of galaxies. We determine the relation between the hi line-width from single-dish observations and the dark matter halo mass ($M_{200}$) inferred from rotation curve fits in the SPARC database, then we apply this relation to galaxies from the hi Parkes All Sky Survey (HIPASS) to derive the HMF. This empirical HMF is well fit by a Schecther function, and matches that expected in $Lambda$CDM over the range $10^{10.5} < M_{200} < 10^{12};mathrm{M}_{odot}$. More massive halos must be poor in neutral gas to maintain consistency with the power law predicted by $Lambda$CDM. We detect no discrepancy at low masses. The lowest halo mass probed by HIPASS, however, is just greater than the mass scale where the Local Group missing satellite problem sets in. The integrated mass density associated with the dark matter halos of hi-detected galaxies sums to $Omega_{rm m,gal} approx 0.03$ over the probed mass range.
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We investigate the origin of the relations between stellar mass and optical circular velocity for early-type (ETG) and late-type (LTG) galaxies --- the Faber-Jackson (FJ) and Tully-Fisher (TF) relations. We combine measurements of dark halo masses (from satellite kinematics and weak lensing), and the distribution of baryons in galaxies (from a new compilation of galaxy scaling relations), with constraints on dark halo structure from cosmological simulations. The principle unknowns are the halo response to galaxy formation and the stellar initial mass function (IMF). The slopes of the TF and FJ relations are naturally reproduced for a wide range of halo response and IMFs. However, models with a universal IMF and universal halo response cannot simultaneously reproduce the zero points of both the TF and FJ relations. For a model with a universal Chabrier IMF, LTGs require halo expansion, while ETGs require halo contraction. A Salpeter IMF is permitted for high mass (sigma > 180 km/s) ETGs, but is inconsistent for intermediate masses, unless V_circ(R_e)/sigma_e > 1.6. If the IMF is universal and close to Chabrier, we speculate that the presence of a major merger may be responsible for the contraction in ETGs while clumpy accreting streams and/or feedback leads to expansion in LTGs. Alternatively, a recently proposed variation in the IMF disfavors halo contraction in both types of galaxies. Finally we show that our models naturally reproduce flat and featureless circular velocity profiles within the optical regions of galaxies without fine-tuning.
We present a Bayesian Stacking technique to directly measure the HI mass function (HIMF) and its evolution with redshift using galaxies formally below the nominal detection threshold. We generate galaxy samples over several sky areas given an assumed HIMF described by a Schechter function and simulate the HI emission lines with different levels of background noise to test the technique. We use Multinest to constrain the parameters of the HIMF in a broad redshift bin, demonstrating that the HIMF can be accurately reconstructed, using the simulated spectral cube far below the HI mass limit determined by the $5sigma$ flux-density limit, i.e. down to $M_{rm HI} = 10^{7.5}$ M$_{odot}$ over the redshift range $0 < z < 0.55$ for this particular simulation, with a noise level similar to that expected for the MIGHTEE survey. We also find that the constraints on the parameters of the Schechter function, $phi_{star}$, $M_star$ and $alpha$ can be reliably fit, becoming tighter as the background noise decreases as expected, although the constraints on the redshift evolution are not significantly affected. All the parameters become better constrained as the survey area increases. In summary, we provide an optimal method for estimating the HI mass at cosmological distances that allows us to constrain the HI mass function below the detection threshold in forthcoming HI surveys. This study is a first step towards the measurement of the HIMF at high ($z>0.1$) redshifts.
We present a new approach in the study of the Initial Mass function (IMF) in external galaxies based on quasar microlensing observations. We use measurements of quasar microlensing magnifications in 24 lensed quasars to estimate the average mass of the stellar population in the lens galaxies without any a priori assumption on the shape of the IMF. The estimated mean mass of the stars is $langle M rangle =0.16^{+0.05}_{-0.08} M_odot$ (at 68% confidence level). We use this average mass to put constraints into two important parameters characterizing the IMF of lens galaxies: the low-mass slope, $alpha_2$, and the low-mass cutoff, $M_{low}$. Combining these constraints with prior information based on lensing, stellar dynamics, and absorption spectral feature analysis, we calculate the posterior probability distribution for the parameters $M_{low}$ and $alpha_2$. We estimate values for the low-mass end slope of the IMF $langle alpha_2rangle=-2.6pm 0.9$ (heavier than that of the Milky Way) and for the low-mass cutoff $langle M_{low}rangle=0.13pm0.07$. These results are in good agreement with previous studies on these parameters and remain stable against the choice of different suitable priors.
The aim of our analysis is twofold. On the one hand we are interested in addressing whether a sample of ETGs morphologically selected differs from a sample of passive galaxies in terms of galaxy statistics. On the other hand we study how the relative abundance of galaxies, the number density and the stellar mass density for different morphological types change over the redshift range 0.6<z<2.5. From the 1302 galaxies brighter than Ks=22 selected from the GOODS-MUSIC catalogue, we classified the ETGs on the basis of their morphology and the passive galaxies on the basis of their sSFR. We proved how the definition of passive galaxy depends on the IMF adopted in the models and on the assumed sSFR threshold. We find that ETGs cannot be distinguished from the other morphological classes on the basis of their low sSFR, irrespective of the IMF adopted in the models. Using the sample of 1302 galaxies morphologically classified into spheroidal galaxies (ETGs) and not spheroidal galaxies (LTGs), we find that their fractions are constant over the redshift range 0.6<z<2.5 (20-30% ETGs vs 70-80% LTGs). However, at z<1 these fractions change among the population of the most massive (M*>=10^(11) M_sol) galaxies, with the fraction of massive ETGs rising up to 40% and the fraction of massive LTGs decreasing down to 60%. Moreover, we find that the number density and the stellar mass density of the whole population of massive galaxies increase almost by a factor of ~10 between 0.6<z<2.5, with a faster increase of these densities for the ETGs than for the LTGs. Finally, we find that the number density of the highest-mass galaxies (M*>3-4x10^(11) M_sol) both ETGs and LTGs do not increase since z~2.5, contrary to the lower mass galaxies. This suggests that the population of the most massive galaxies formed at z>2.5-3 and that the assembly of such high-mass galaxies is not effective at lower redshift.
[Abridged] Tight correlations between supermassive black hole (SMBH) mass ($M_{rm BH}$) and the properties of the host galaxy have useful implications for our understanding of the growth of SMBHs and evolution of galaxies. Here, we present newly observed correlations between $M_{rm BH}$ and the host galaxy total UV$-$ [3.6] color ($mathcal{C_{rm UV,tot}}$, Pearsons r = $0.6-0.7$) for a sample of 67 galaxies (20 early-type galaxies and 47 late-type galaxies) with directly measured $M_{rm BH}$ in the GALEX/S$^{4}$G survey. The colors are carefully measured in a homogeneous manner using the galaxies FUV, NUV and 3.6 $micron$ magnitudes and their multi-component structural decompositions in the literature. We find that more massive SMBHs are hosted by (early- and late-type) galaxies with redder colors, but the $M_{rm BH}- mathcal{C_{rm UV,tot}}$ relations for the two morphological types have slopes that differ at $sim 2 sigma$ level. Early-type galaxies define a red sequence in the $M_{rm BH}- mathcal{C_{rm UV,tot}}$ diagrams, while late-type galaxies trace a blue sequence. Within the assumption that the specific star formation rate of a galaxy (sSFR) is well traced by $L_{rm UV}/L_{rm 3.6}$, it follows that the SMBH masses for late-type galaxies exhibit a steeper dependence on sSFR than those for early-type galaxies. The $M_{rm BH}- mathcal{C_{rm UV,tot}}$ and $M_{rm BH}-L_{rm 3.6,tot}$ relations for the sample galaxies reveal a comparable level of vertical scatter in the log $M_{rm BH}$ direction, roughly $5%-27%$ more than the vertical scatter of the $M_{rm BH}-sigma$ relation. Our $M_{rm BH}- mathcal{C_{rm UV,tot}}$ relations suggest different channels of SMBH growth for early- and late-type galaxies, consistent with their distinct formation and evolution scenarios.
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