arXiv subjects

M. Clausen

Publications and source records attributed to M. Clausen.

5 recordsLinked to original sources

arXiv2025

The JWST Emission Line Survey (JELS): The sizes and merger fraction of star-forming galaxies during the Epoch of Reionization

We used observations from the JWST Emission Line Survey (JELS) to measure the half-light radii ($r_{e}$) of 23 H$\alpha$-emitting star-forming (SF) galaxies at $z=6.1$ in the PRIMER/COSMOS field. Galaxy sizes were measured in JWST Near-infrared Camera observations in rest-frame H$\alpha$ (tracing recent star formation) with the F466N and F470N narrowband filters from JELS, and compared against rest-$R$-band, $V$-band (tracing established stellar populations) and near-ultraviolet sizes. We find a size-stellar mass ($r_{e}-M_{*}$) relationship with a slope that is consistent with literature values at lower redshifts, though offset to lower sizes. We observe a large scatter in $r_{e}$ at low stellar mass ($M_{*}<10^{8.4}$ M$_{\odot}$) which we believe is the result of bursty star formation histories (SFHs) of SF galaxies at the Epoch of Reionization (EoR). We find that the stellar and ionised gas components are similar in size at $z=6.1$. The evidence of already-established stellar components in these H$\alpha$ emitters (HAEs) indicates previous episodes of star formation have occurred. As such, following other JELS studies finding our HAEs are undergoing a current burst of star formation, we believe our results indicate that SF galaxies at the end of the EoR have already experienced a bursty SFH. From our $r_{e}-M_{*}$ relationship, we find $r_{e, \text{F444W}}=0.76\pm0.46$ kpc for fixed stellar mass $M_{*}=10^{9.25}$ M$_{\odot}$, which is in agreement with other observations and simulations of star forming galaxies in the literature. We find a close-pair (major) merger fraction of ($f_{\text{maj. merger}}=0.44\pm0.22$) $f_{\text{merger}}=0.43\pm0.11$ for galaxy separations $d\lesssim25$ kpc, which is in agreement with other $z\approx6$ studies.

astro-ph.GA↗

arXiv2024

The JWST Emission Line Survey (JELS): An untargeted search for H$\alpha$ emission line galaxies at $z > 6$ and their physical properties

We present the first results of the JWST Emission Line Survey (JELS). Utilising the first NIRCam narrow-band imaging at 4.7$\mu$m, over 63 arcmin$^{2}$ in the PRIMER/COSMOS field, we identified 609 emission line galaxy candidates. From these, we robustly selected 35 H$\alpha$ star-forming galaxies at $z \sim 6.1$, with H$\alpha$ star-formation rates ($\rm{SFR_{H\alpha}}$) $\sim0.9-15\ \rm{M_{\odot} \ yr^{-1}}$. Combining our unique H$\alpha$ sample with the exquisite panchromatic data in the field, we explored their physical properties and star-formation histories, and compared these to a broad-band selected sample at $z\sim 6$ which offered vital new insights into the nature of high-redshift galaxies. UV-continuum slopes ($\beta$) were considerably redder for our H$\alpha$ sample ($\langle\beta\rangle\sim-1.92$) compared to the broad-band sample ($\langle\beta\rangle\sim-2.35$). This was not due to dust attenuation as our H$\alpha$ sample was relatively dust-poor (median $A_V=0.23$); instead, we argued the reddened slopes could be due to nebular continuum. We compared $\rm{SFR_{H\alpha}}$ and the UV-continuum-derived $\rm{SFR_{UV}}$ to SED-fitted measurements averaged over canonical timescales of 10 and 100 Myr ($\rm{SFR_{10}}$ and $\rm{SFR_{100}}$). We found an increase in recent SFR for our sample of H$\alpha$ emitters, particularly at lower stellar masses ($<10^9 \ \rm{M_{\odot}}$). We also found $\rm{SFR_{H\alpha}}$ strongly traced SFR averaged over 10 Myr timescales, whereas the UV-continuum over-predicts SFR on 100 Myr timescales at low stellar masses. These results point to our H$\alpha$ sample undergoing `bursty' star formation. Our F356W $z \sim 6$ sample showed a larger scatter in $\rm{SFR_{10}/SFR_{100}}$ across all stellar masses, which highlighted how narrow-band photometric selections of H$\alpha$ emitters are key to quantifying the burstiness of star-formation activity.

astro-ph.GA↗

arXiv2024

The JWST Emission Line Survey (JELS): Extending rest-optical narrow-band emission line selection into the Epoch of Reionization

We present the JWST Emission Line Survey (JELS), a JWST imaging programme exploiting the wavelength coverage and sensitivity of NIRCam to extend narrow-band rest-optical emission line selection into the epoch of reionization (EoR) for the first time, and to enable unique studies of the resolved ionised gas morphology in individual galaxies across cosmic history. The primary JELS observations comprise $\sim4.7\mu$m narrow-band imaging over $\sim63$ arcmin$^{2}$ designed to enable selection of H$\alpha$ emitters at z~6.1 and a host of novel emission-line samples, including [OIII] ($z\sim8.3$) and Paschen $\alpha/\beta$ ($z\sim1.5/2.8$). For the F466N/F470N narrow-band observations, the emission-line sensitivities achieved are up to $\sim2\times$ more sensitive than current slitless spectroscopy surveys (5$\sigma$ limits of 0.8-1.2$\times10^{-18}\,\text{erg s}^{-1}\text{cm}^{-2}$), corresponding to unobscured H$\alpha$ star-formation rates (SFRs) of 0.9-1.3 $\text{M}_{\odot}\text{yr}^{-1}$ at z~6.1, extending emission-line selections in the EoR to fainter populations. Simultaneously, JELS also adds F200W broadband and F212N narrow-band imaging (H$\alpha$ at z~2.23) that probes SFRs $\gtrsim5\times$ fainter than previous ground-based narrow-band studies ($\sim0.2\text{M}_{\odot}\text{yr}^{-1}$), offering an unprecedented resolved view of star formation at cosmic noon. We present the detailed JELS survey design, key data processing steps specific to the survey observations, and demonstrate the exceptional data quality and imaging sensitivity achieved. We then summarise the key scientific goals of JELS, demonstrate the precision and accuracy of the expected redshift and measured emission line recovery through detailed simulations, and present examples of spectroscopically confirmed H$\alpha$ and [OIII] emitters discovered by JELS that illustrate the novel parameter space probed.

astro-ph.GA↗

arXiv2001

COSMIC - The SLAC COntrol System MIgration Challenge

The current SLC control system was designed and constructed over 20 years ago. Many of the technologies on which it was based are obsolete and difficult to maintain. The VMS system that forms the core of the Control System is still robust but third party applications are almost non-existent and its long-term future is in doubt. The need for a Control System at SLAC that can support experiments for the foreseeable future is not in doubt. The present B-Factory or PEPII experiment is projected to run at least 10 years. An FEL laser of unprecedented intensity plus an ongoing series of fixed target experiments is also in our future. The Next Linear Collider or NLC may also be in our future although somewhat farther distant in time. The NLC has performance requirements an order of magnitude greater than anything we have built to date. In addition to large numbers of IOCs and process variables, Physicists would like to archive everything all the time. This makes the NLC Control System a bit like a detector system as well. The NLC Control System will also need the rich suite of accelerator applications that are available with the current SLC Control System plus many more that are now only a glimmer in the eyes of Accelerator Physicists. How can we migrate gradually away from the current SLC Control System towards a design that will scale to the NLC while keeping everything operating smoothly for the ongoing experiments?

physics.acc-ph↗

arXiv2001

Upgrading of the beam diagnostic system of U-70 beam transfer lines

The beam diagnostic system of U-70 beam transfer lines (beam profiles, intensity and beam losses measurements) was designed in the beginning of 80-th on the base of 8-bit microprocessor, SUMMA hardware and home made serial communication link. Because of the maintenance problems the decision was taken to upgrade the hardware and software parts of the system.

physics.ins-det↗