Prof. Matt Jarvis

Abstract:

We present a novel 2D flux density model for observed H i emission lines combined with a Bayesian stacking technique to measure the baryonic Tully-Fisher relation below the nominal detection threshold. We simulate a galaxy catalogue, which includes H i lines described with either Gaussian or busy function profiles, and H i data cubes with a range of noise and survey areas similar to the MeerKAT International Giga-Hertz Tiered Extragalactic Exploration (MIGHTEE) survey. With prior knowledge of redshifts, stellar masses, and inclinations of spiral galaxies, we find that our model can reconstruct the input baryonic Tully-Fisher parameters (slope and zero-point) most accurately in a relatively broad redshift range from the local Universe to z = 0.3 for all the considered levels of noise and survey areas and up to z = 0.55 for a nominal noise of 90 μJy/channel over 5 deg2. Our model can also determine the MHI - M∗ relation for spiral galaxies beyond the local Universe and account for the detailed shape of the H I emission line, which is crucial for understanding the dynamics of spiral galaxies. Thus, we have developed a Bayesian stacking technique for measuring the baryonic Tully-Fisher relation for galaxies at low stellar and/or H I masses and/or those at high redshift, where the direct detection of H I requires prohibitive exposure times.

Abstract:

Using a sample of 67 galaxies from the MeerKAT International GigaHertz Tiered Extragalactic Exploration Survey Early Science data, we study the H i-based baryonic Tully-Fisher relation (bTFr), covering a period of ∼1 billion years (0 ≤ z ≤ 0.081). We consider the bTFr based on two different rotational velocity measures: The width of the global H i profile and Vout, measured as the outermost rotational velocity from the resolved H i rotation curves. Both relations exhibit very low intrinsic scatter orthogonal to the best-fitting relation (σ⊥ = 0.07 ± 0.01), comparable to the SPARC sample at z 0. The slopes of the relations are similar and consistent with the z 0 studies (3.66+0.35-0.29 for W50 and 3.47+0.37-0.30 for Vout). We find no evidence that the bTFr has evolved over the last billion years, and all galaxies in our sample are consistent with the same relation independent of redshift and the rotational velocity measure. Our results set-up a reference for all future studies of the H i-based bTFr as a function of redshift that will be conducted with the ongoing deep SKA pathfinders surveys.

Abstract:

We study the radio spectral properties of 2094 star-forming galaxies (SFGs) by combining our early science data from the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey with VLA, GMRT radio data, and rich ancillary data in the COSMOS field. These SFGs are selected at VLA 3 GHz, and their flux densities from MeerKAT 1.3 GHz and GMRT 325 MHz imaging data are extracted using the ‘superdeblending’ technique. The median radio spectral index is α3GHz1.3GHz=−0.80±0.01 without significant variation across the rest-frame frequencies ∼1.3–10 GHz, indicating radio spectra dominated by synchrotron radiation. On average, the radio spectrum at observer-frame 1.3–3 GHz slightly steepens with increasing stellar mass with a linear fitted slope of β = −0.08 ± 0.01, which could be explained by age-related synchrotron losses. Due to the sensitivity of GMRT 325 MHz data, we apply a further flux density cut at 3 GHz (⁠S3GHz≥50μJy) and obtain a sample of 166 SFGs with measured flux densities at 325 MHz, 1.3 GHz, and 3 GHz. On average, the radio spectrum of SFGs flattens at low frequency with the median spectral indices of α1.3GHz325MHz=−0.59+0.02−0.03 and α3.0GHz1.3GHz=−0.74+0.01−0.02⁠. At low frequency, our stacking analyses show that the radio spectrum also slightly steepens with increasing stellar mass. By comparing the far-infrared-radio correlations of SFGs based on different radio spectral indices, we find that adopting α3GHz1.3GHz for k-corrections will significantly underestimate the infrared-to-radio luminosity ratio (qIR) for >17 per cent of the SFGs with measured flux density at the three radio frequencies in our sample, because their radio spectra are significantly flatter at low frequency (0.33–1.3 GHz).

Abstract:

We present the serendipitous discovery of a galaxy group in the XMM-LSS field with MIGHTEE Early Science observations. 20 galaxies are detected in H I in this z ∼ 0.044 group, with a 3σ column density sensitivity of NHI=1.6×1020cm−2⁠. This group has not been previously identified, despite residing in a well-studied extragalactic legacy field. We present spatially resolved H I total intensity and velocity maps for each of the objects which reveal environmental influence through disturbed morphologies. The group has a dynamical mass of log10(Mdyn/M⊙)=12.32⁠, and is unusually gas-rich, with an H I-to-stellar mass ratio of log10(f∗HI)=−0.2⁠, which is 0.7 dex greater than expected. The group’s high H I content, spatial, velocity, and identified galaxy type distributions strongly suggest that it is in the early stages of its assembly. The discovery of this galaxy group is an example of the importance of mapping spatially resolved H I in a wide range of environments, including galaxy groups. This scientific goal has been dramatically enhanced by the high sensitivity, large field-of-view, and wide instantaneous bandwidth of the MeerKAT telescope.

Abstract:

Utilizing optical and near-infrared broad-band photometry covering >5 deg2 in two of the most well-studied extragalactic legacy fields (COSMOS and XMM-LSS), we measure the galaxy stellar mass function (GSMF) between 0.1 < z < 2.0. We explore in detail the effect of two source extraction methods (SExtractor and ProFound) in addition to the inclusion/exclusion of Spitzer IRAC 3.6 and 4.5 μm photometry when measuring the GSMF. We find that including IRAC data reduces the number of massive (log10(M/M⊙) > 11.25) galaxies found due to improved photometric redshift accuracy, but has little effect on the more numerous lower-mass galaxies. We fit the resultant GSMFs with double Schechter functions down to log10(M/M⊙) = 7.75 (9.75) at z = 0.1 (2.0) and find that the choice of source extraction software has no significant effect on the derived best-fitting parameters. However, the choice of methodology used to correct for the Eddington bias has a larger impact on the high-mass end of the GSMF, which can partly explain the spread in derived M* values from previous studies. Using an empirical correction to model the intrinsic GSMF, we find evidence for an evolving characteristic stellar mass with δlog10(M*/M⊙)/δz = −0.16±0.05(−0.11±0.05)⁠, when using SExtractor (ProFound). We argue that with widely quenched star formation rates in massive galaxies at low redshift (z < 0.5), additional growth via mergers is required in order to sustain such an evolution to a higher characteristic mass.