Galaxy formation and evolution

Abstract:

© 2019. The American Astronomical Society. All rights reserved. We present resolved [C i] line intensities of 18 nearby galaxies observed with the SPIRE FTS spectrometer on the Herschel Space Observatory. We use these data along with resolved CO line intensities from J up = 1 to 7 to interpret what phase of the interstellar medium the [C i] lines trace within typical local galaxies. A tight, linear relation is found between the intensities of the CO(4-3) and [C i](2-1) lines; we hypothesize this is due to the similar upper level temperature of these two lines. We modeled the [C i] and CO line emission using large-velocity gradient models combined with an empirical template. According to this modeling, the [C i](1-0) line is clearly dominated by the low-excitation component. We determine [C i] to molecular mass conversion factors for both the [C i](1-0) and [C i](2-1) lines, with mean values of α [C i](1-0) = 7.3 M o K-1 km-1 s pc-2 and α [C i](2-1) = 34 M o K-1 km-1 s pc-2 with logarithmic root-mean-square spreads of 0.20 and 0.32 dex, respectively. The similar spread of α [C I](1-0) to αCO (derived using the CO(2-1) line) suggests that [C i](1-0) may be just as good a tracer of cold molecular gas as CO(2-1) in galaxies of this type. On the other hand, the wider spread of α [C i](2-1) and the tight relation found between [C i](2-1) and CO(4-3) suggest that much of the [C i](2-1) emission may originate in warmer molecular gas.

Abstract:

We present 1–10 GHz radio continuum flux density, spectral index, polarization, and rotation measure (RM) images of the youngest known Galactic supernova remnant (SNR) G1.9+0.3, using observations from the Australia Telescope Compact Array. We have conducted an expansion study spanning eight epochs between 1984 and 2017, yielding results consistent with previous expansion studies of G1.9+0.3. We find a mean radio continuum expansion rate of (0.78 ± 0.09) per cent yr−1 (or ∼8900 km s−1 at an assumed distance of 8.5 kpc), although the expansion rate varies across the SNR perimetre. In the case of the most recent epoch between 2016 and 2017, we observe faster-than-expected expansion of the northern region. We find a global spectral index for G1.9+0.3 of −0.81 ± 0.02 (76 MHz–10 GHz). Towards the northern region, however, the radio spectrum is observed to steepen significantly (∼−1). Towards the two so-called (east and west) ‘ears’ of G1.9+0.3, we find very different RM values of 400–600 and 100–200 rad m2, respectively. The fractional polarization of the radio continuum emission reaches (19 ± 2) per cent, consistent with other, slightly older, SNRs such as Cas A.

Abstract:

Mapping of the large-scale structure through cosmic time has numerous applications in the studies of cosmology and galaxy evolution. At $z > 2$, the structure can be traced by the neutral intergalactic medium (IGM) by way of observing the Ly$\alpha$, forest towards densely-sampled lines-of-sight of bright background sources, such as quasars and star forming galaxies. We investigate the scientific potential of MOSAIC, a planned multi-object spectrograph on the European Extremely Large Telescope (ELT), for the 3D mapping of the IGM at $z \gtrsim 3$. We simulate a survey of $3 \lesssim z \lesssim 4$ galaxies down to a limiting magnitude of $m_{r}\sim 25.5$ mag in an area of 1 degree$^2$ in the sky. Galaxies and their spectra (including the line-of-sight Ly$\alpha$ absorption) are taken from the lightcone extracted from the Horizon-AGN cosmological hydrodynamical simulation. The quality of the reconstruction of the original density field is studied for different spectral resolutions and signal-to-noise ratios of the spectra. We demonstrate that the minimum $S/N$ (per resolution element) of the faintest galaxies that such survey has to reach is $S/N = 4$. We show that a survey with such sensitivity enables a robust extraction of cosmic filaments and the detection of the theoretically-predicted galaxy stellar mass and star-formation rate gradients towards filaments. By simulating the realistic performance of MOSAIC we obtain $S/N(T_{\rm obs}, R, m_{r})$ scaling relations. We estimate that $\lesssim 35~(65)$ nights of observation time are required to carry out the survey with the instrument's high multiplex mode and with the spectral resolution of $R=1000~(2000)$. A survey with a MOSAIC-concept instrument on the ELT is found to enable the mapping of the IGM at $z > 3$ on Mpc scales, and as such will be complementary to and competitive with other planned IGM tomography surveys. [abridged]