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Register a new userExploring the evidence for a large local void with supernovae Ia data
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Added by
Vladimir Lukovic Vukosav
Publication date
2019
fields
Physics
and research's language is
English
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In this work we utilise the most recent publicly available type Ia supernova (SN Ia) compilations and implement a well formulated cosmological model based on Lema^{i}tre-Tolman-Bondi metric in presence of cosmological constant $Lambda$ ($Lambda$LTB) to test for signatures of large local inhomogeneities at $zleq0.15$. Local underdensities in this redshift range have been previously found based on luminosity density (LD) data and galaxy number counts. Our main constraints on the possible local void using the Pantheon SN Ia dataset are: redshift size of $z_{rm size}=0.068^{+0.021}_{-0.030}$; density contrast of $deltaOmega_0/Omega_0=-10.5_{-7.4}^{+9.3}%$ between 16th and 84th percentiles. Investigating the possibility to alleviate the $sim9%$ disagreement between measurements of present expansion rate $H_0$ coming from calibrated local SN Ia and high-$z$ cosmic microwave background data, we find large local void to be a very unlikely explanation alone, consistently with previous studies. However, the level of matter inhomogeneity at a scale of $sim$100Mpc that is allowed by SN Ia data, although not expected from cosmic variance calculations in standard model of cosmology, could be the origin of additonal systematic error in distance ladder measurements based on SN Ia. Fitting low-redshift Pantheon data with a cut $0.023<z<0.15$ to the $Lambda$LTB model and to the Taylor expanded luminosity distance formula we estimate that this systematic error amounts to $1.1%$ towards the lower $H_0$ value. A test for local anisotropy in Pantheon SN Ia data yields null evidence. Analysis of LD data provides a constraint on contrast of large isotropic void $deltaOmega_0/Omega_0=-51.9%pm6.3%$, which is in $sim4sigma$ tension with SN Ia results. More data are necessary to better constrain the local matter density profile and understand the disagreement between SN and LD samples
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We use multi-wavelength, matched aperture, integrated photometry from GALEX, SDSS and the RC3 to estimate the physical properties of 166 nearby galaxies hosting 168 well-observed Type Ia supernovae (SNe Ia). Our data corroborate well-known features that have been seen in other SN Ia samples. Specifically, hosts with active star formation produce brighter and slower SNe Ia on average, and hosts with luminosity-weighted ages older than 1 Gyr produce on average more faint, fast and fewer bright, slow SNe Ia than younger hosts. New results include that in our sample, the faintest and fastest SNe Ia occur only in galaxies exceeding a stellar mass threshhold of ~10^10 M_sun, indicating that their progenitors must arise in populations that are older and/or more metal rich than the general SN Ia population. A low host extinction sub-sample hints at a residual trend in peak luminosity with host age, after correcting for light-curve shape, giving the appearance that older hosts produce less-extincted SNe Ia on average. This has implications for cosmological fitting of SNe Ia and suggests that host age could be useful as a parameter in the fitting. Converting host mass to metallicity and computing 56Ni mass from the supernova light curves, we find that our local sample is consistent with a model that predicts a shallow trend between stellar metallicity and the 56Ni mass that powers the explosion, but we cannot rule out the absence of a trend. We measure a correlation between 56Ni mass and host age in the local universe that is shallower and not as significant as that seen at higher redshifts. The details of the age -- 56Ni mass correlations at low and higher redshift imply a luminosity-weighted age threshhold of ~3 Gyr for SN Ia hosts, above which they are less likely to produce SNe Ia with 56Ni masses above ~0.5 M_sun. (Abridged)
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Recent cosmological modeling efforts have shown that a local underdensity on scales of a few hundred Mpc (out to z ~ 0.1), could produce the apparent acceleration of the expansion of the universe observed via type Ia supernovae. Several studies of galaxy counts in the near-infrared (NIR) have found that the local universe appears under-dense by ~25-50% compared with regions a few hundred Mpc distant. Galaxy counts at low redshifts sample primarily L ~ L* galaxies. Thus, if the local universe is under-dense, then the normalization of the NIR galaxy luminosity function (LF) at z>0.1 should be higher than that measured for z<0.1. Here we present a highly complete (> 90%) spectroscopic sample of 1436 galaxies selected in the H-band to study the normalization of the NIR LF at 0.1<z<0.3 and address the question of whether or not we reside in a large local underdensity. We find that for the combination of our six fields, the product phi* L* at 0.1 < z < 0.3 is ~ 30% higher than that measured at lower redshifts. While our statistical errors in this measurement are on the ~10% level, we find the systematics due to cosmic variance may be larger still. We investigate the effects of cosmic variance on our measurement using the COSMOS cone mock catalogs from the Millennium simulation and recent empirical estimates. We find that our survey is subject to systematic uncertainties due to cosmic variance at the 15% level ($1 sigma), representing an improvement by a factor of ~ 2 over previous studies in this redshift range. We conclude that observations cannot yet rule out the possibility that the local universe is under-dense at z<0.1.
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