arXiv subjects

K. Knudsen

Publications and source records attributed to K. Knudsen.

5 recordsLinked to original sources

arXiv2026

Investigating the role of turbulence in the interstellar medium in $z\sim3$ dusty star-forming galaxies using kpc-resolution ALMA dust and gas maps

We present ALMA high-resolution ($\sim$0.25$^{\prime\prime}$/2 kpc) CO(5-4) and CO(4-3) observations of three $z\sim 3$ submillimetre-selected dusty galaxies from the ALESS survey. These data complement existing [sub]-kpc scale ALMA 870$\mu$m continuum imaging and JWST NIRCam and MIRI imaging from the ALESS-JWST program, allowing us to trace the molecular gas, dust-obscured star formation, and stellar populations on similar spatial scales. We spectroscopically confirm that two of the sources lie at the same redshift and are likely interacting. We find that the molecular-gas distribution broadly follows the dusty star-forming structures seen in the 870$\mu$m dust continuum imaging, but that the gas reservoirs are significantly more extended than the dust emission with a spatial extent comparable to the rest-frame near-infrared stellar emission. By modeling the kinematics for the two highest signal-to-noise sources, we find that the galaxies are well-fit by rotating disc models with high ratios of ordered to random motion ($V_{\rm{max}}/\overline{\sigma}=5\pm1$ and $6\pm1$), although smaller-scale kinematic deviations cannot be ruled out at the current sensitivity and spatial resolution. Finally, utilizing the high-resolution 870$\mu$m dust continuum and CO data, we investigate star-formation scaling relations on kpc-scales in these high-redshift galaxies. Assuming a constant CO-to-H$_{2}$ conversion factor and excitation ratio, we find that the data are offset from theoretical star-formation relation predictions that do not take turbulence into account, but consistent with gravo-turbulent models, thereby suggesting that turbulence plays a central role in regulating star formation at high redshift.

astro-ph.GA↗

arXiv2025

Resolving the molecular gas emission of the z~2.5-2.8 starburst galaxies SPT0125-47 and SPT 2134-50

The comoving cosmic star formation rate density peaks at z~2-3, with dusty star-forming galaxies being significant contributors to this peak. These galaxies are characterized by their high star formation rates and substantial infrared luminosities. The formation mechanisms remain an open question for these galaxies, particularly with respect to how such intense levels of star formation are triggered and maintained. We aim to resolve CO(3-2) emission toward two strongly lensed galaxies, SPT0125-47 and SPT2134-50, at z~2.5-2.8 to determine their morphology and physical properties. We used high-resolution ALMA band 3 observations of CO(3-2) emission toward both sources to investigate their properties. We performed parametric and nonparametric lens modeling using the publicly available lens modeling software PyAutoLens. We divided the CO(3-2) emission line into two bins corresponding to the red and blue portions of the emission line and nonparametrically modeled the source plane emission for both bins. We performed a basic analysis of the morphology and kinematics in the source plane using nonparametric lens modeling of the red and blue bins. We found tentative evidence of a velocity gradient across both sources and no evidence of any clumpy structure, companions, or ongoing mergers. The previously calculated high star formation rates and low depletion times of both SPT0125-47 and SPT2134-50 suggest that these galaxies are undergoing a dramatic phase in their evolution. Given the lack of evidence of ongoing interactions or mergers in our source plane models, we suggest that the intense star formation was triggered by a recent interaction and/or merger. We also consider the possibility that these galaxies might be in the process of settling into disks.

astro-ph.GA↗

arXiv2022

Detection of companion galaxies around hot dust-obscured hyper-luminous galaxy W0410-0913

The phase transition between galaxies and quasars is often identified with the rare population of hyper-luminous, hot dust-obscured galaxies. Galaxy formation models predict these systems to grow via mergers, that can deliver large amounts of gas toward their centers, induce intense bursts of star formation and feed their supermassive black holes. Here we report the detection of 24 galaxies emitting Lyman-alpha emission on projected physical scales of about 400 kpc around the hyper-luminous hot dust-obscured galaxy W0410-0913, at redshift z = 3.631, using Very Large Telescope observations. While this indicates that W0410-0913 evolves in a very dense environment, we do not find clear signs of mergers that could sustain its growth. Data suggest that if mergers occurred, as models expect, these would involve less massive satellites, with only a moderate impact on the internal interstellar medium of W0410-0913, which is sustained by a rotationally-supported fast-rotating molecular disk, as Atacama Large Millimeter Array observations suggest.

astro-ph.GA↗

arXiv2022

CONCERTO: High-fidelity simulation of millimeter line emissions of galaxies and [CII] intensity mapping

The intensity mapping of the [CII] 158um line redshifted to the sub-mm window is a promising probe of the z>4 star formation and its spatial distribution into the large-scale structure. To prepare the first-generation experiments (e.g., CONCERTO), we need realistic simulations of the sub-mm extragalactic sky in spectroscopy. We present a new version of the SIDES simulation including the main sub-mm lines around 1mm (CO, [CII], [CI]). This approach successfully reproduces the observed line luminosity functions. We then use our simulation to generate CONCERTO-like cubes (125-305GHz) and forecast the power spectra of the fluctuations caused by the various astrophysical components at those frequencies. Depending on our assumptions on the relation between star formation rate and [CII] luminosity, and the star formation history, our predictions of the z~6 [CII] power spectrum vary by two orders of magnitude. This highlights how uncertain the predictions are and how important future measurements will be to improve our understanding of this early epoch. SIDES can reproduce the CO shot noise recently measured at ~100 GHz by the mmIME experiment. Finally, we compare the contribution of the different astrophysical components at various redshift to the power spectra. The continuum is by far the brightest, by a factor of 3 to 100 depending on the frequency. At 300GHz, the CO foreground power spectrum is higher than the [CII] one for our base scenario. At lower frequency, the contrast between [CII] and extragalactic foregrounds is even worse. Masking the known galaxies from deep surveys should allow to reduce the foregrounds to 20% of the [CII] power spectrum up to z~6.5. However, this masking method will not be sufficient at higher redshifts. The code and the products of our simulation are released publicly and can be used for both intensity mapping experiments and sub-mm continuum and line surveys.

astro-ph.GA↗

arXiv2021

The Evolution of the IR Luminosity Function and Dust-obscured Star Formation in the Last 13 Billion Years

We present the first results from the 2mm Mapping Obscuration to Reionization (MORA) survey, the largest ALMA contiguous blank-field survey to-date with a total area of 184 sq. arcmin and the only at 2mm to search for dusty star-forming galaxies (DSFGs). We use the 13 sources detected above 5sigma to estimate the first ALMA galaxy number counts at this wavelength. These number counts are then combined with the state-of-the-art galaxy number counts at 1.2mm and 3mm and with a backward evolution model to place constraints on the evolution of the IR luminosity function and dust-obscured star formation in the last 13 billion years. Our results suggest a steep redshift evolution on the space density of DSFGs and confirm the flattening of the IR luminosity function at faint luminosities, with a slope of $α_{LF} = -0.42^{+0.02}_{-0.04}$. We conclude that the dust-obscured component, which peaks at z=2-2.5, has dominated the cosmic history of star formation for the past ~12 billion years, back to z~4. At z=5, the dust-obscured star formation is estimated to be ~35% of the total star formation rate density and decreases to 25%-20% at z=6-7, implying a minor contribution of dust-enshrouded star formation in the first billion years of the Universe. With the dust-obscured star formation history constrained up to the end of the epoch of reionization, our results provide a benchmark to test galaxy formation models, to study the galaxy mass assembly history, and to understand the dust and metal enrichment of the Universe at early times.

astro-ph.GA↗