ChinaXiv.org 中国科学院科技论文预发布平台

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2023
9

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Astrophysical processes
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1. ChinaXiv:202303.04356
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DESI Observations of the Andromeda Galaxy: Revealing the Immigration History of our Nearest Neighbor

Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19

Arjun Dey Joan R. Najita S. E. Koposov J. Josephy-Zack Gabriel Maxemin Eric F. Bell C. Poppett E. Patel L. Beraldo e Silva A. Raichoor D. Schlegel D. Lang A. Meisner Adam D. Myers J. Aguilar S. Ahlen C. Allende Prieto D. Brooks A. P. Cooper K. S. Dawson

Abstract： We present DESI observations of the inner halo of M31, which reveal the kinematics of a recent merger - a galactic immigration event - in exquisite detail. Of the 11,416 sources studied in 3.75 hour of on-sky exposure time, 7,438 are M31 sources with well measured radial velocities. The observations reveal intricate coherent kinematic structure in the positions and velocities of individual stars: streams, wedges, and chevrons. While hints of coherent structures have been previously detected in M31, this is the first time they have been seen with such detail and clarity in a galaxy beyond the Milky Way. We find clear kinematic evidence for shell structures in the Giant Stellar Stream, the Northeast Shelf and Western Shelf regions. The kinematics are remarkably similar to the predictions of dynamical models constructed to explain the spatial morphology of the inner halo. The results are consistent with the interpretation that much of the substructure in the inner halo of M31 is produced by a single galactic immigration event 1 - 2 Gyr ago. Significant numbers of metal-rich stars ([Fe/H]$>-0.5$) are present in all of the detected substructures, suggesting that the immigrating galaxy had an extended star formation history. We also investigate the ability of the shells and Giant Stellar Stream to constrain the gravitational potential of M31, and estimate the mass within a projected radius of 125 kpc to be ${\rm log_{10}}\, M_{\rm NFW}(<125\,{\rm kpc})/M_\odot = 11.80_{-0.10}^{+0.12}$. The results herald a new era in our ability to study stars on a galactic scale and the immigration histories of galaxies.

Peer Review Status:Awaiting Review

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2. ChinaXiv:202303.05433
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Target Selection and Sample Characterization for the DESI LOW-Z Secondary Target Program

Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19

Elise Darragh-Ford John F. Wu Yao-Yuan Mao Risa H. Wechsler Marla Geha Jaime E. Forero-Romero ChangHoon Hahn Nitya Kallivayalil John Moustakas Ethan O. Nadler Marta Nowotka J. E. G. Peek Erik J. Tollerud Benjamin Weiner J. Aguilar S. Ahlen D. Brooks A. P. Cooper A. de la Macorra A. Dey

Abstract： We introduce the DESI LOW-Z Secondary Target Survey, which combines the wide area capabilities of the Dark Energy Spectroscopic Instrument (DESI) with an efficient, low-redshift target selection method. Our selection consists of a set of color and surface brightness cuts, combined with modern machine learning methods, to optimally target low-redshift dwarf galaxies (z < 0.03) between 19 < r < 21. We employ a convolutional neural network (CNN) to select high priority targets. Our data validation shows that the CNN can achieve 90% completeness at z < 0.03 with 20% efficiency at selecting low-redshift galaxies, compared to compared to efficiencies of ~1% using traditional photometric methods. The LOW-Z survey has already obtained over 22,000 redshifts of dwarf galaxies ($M_*$ < $10^9$ $M_\odot$), comparable to the number of dwarf galaxies discovered in SDSS and GAMA. As a spare fiber survey, LOW-Z currently receives fiber allocation for just ~30% of its targets. However, we estimate that our photometric cuts are > 95% complete in target selection at z < 0.03 between 19 展开 -->

Peer Review Status:Awaiting Review

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3. ChinaXiv:202303.02295
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The DESI Survey Validation: Results from Visual Inspection of Bright Galaxies, Luminous Red Galaxies, and Emission Line Galaxies

Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19

Ting-Wen Lan R. Tojeiro E. Armengaud J. Xavier Prochaska T. M. Davis David M. Alexander A. Raichoor Rongpu Zhou Christophe Yeche C. Balland S. BenZvi A. Berti R. Canning A. Carr H. Chittenden S. Cole M. -C. Cousinou K. Dawson Biprateep Dey K. Douglass

Abstract： The Dark Energy Spectroscopic Instrument (DESI) Survey has obtained a set of spectroscopic measurements of galaxies to validate the final survey design and target selections. To assist in these tasks, we visually inspect (VI) DESI spectra of approximately 2,500 bright galaxies, 3,500 luminous red galaxies (LRGs), and 10,000 emission line galaxies (ELGs), to obtain robust redshift identifications. We then utilize the VI redshift information to characterize the performance of the DESI operation. Based on the VI catalogs, our results show that the final survey design yields samples of bright galaxies, LRGs, and ELGs with purity greater than $99\%$. Moreover, we demonstrate that the precision of the redshift measurements is approximately 10 km/s for bright galaxies and ELGs and approximately 40 km/s for LRGs. The average redshift accuracy is within 10 km/s for the three types of galaxies. The VI process also helps improve the quality of the DESI data by identifying spurious spectral features introduced by the pipeline. Finally, we show examples of unexpected real astronomical objects, such as Ly$\alpha$ emitters and strong lensing candidates, identified by VI. These results demonstrate the importance and utility of visually inspecting data from incoming and upcoming surveys, especially during their early operation phases.

Peer Review Status:Awaiting Review

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4. ChinaXiv:202303.03146
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The DESI Survey Validation: Results from Visual Inspection of the Quasar Survey Spectra

Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19

David M. Alexander Tamara M. Davis E. Chaussidon V. A. Fawcett Alma X. Gonzalez-Morales Ting-Wen Lan Christophe Yeche S. Ahlen J. N. Aguilar E. Armengaud S. Bailey D. Brooks Z. Cai R. Canning A. Carr S. Chabanier Marie-Claude Cousinou K. Dawson A. de la Macorra A. Dey

Abstract： A key component of the Dark Energy Spectroscopic Instrument (DESI) survey validation (SV) is a detailed visual inspection (VI) of the optical spectroscopic data to quantify key survey metrics. In this paper we present results from VI of the quasar survey using deep coadded SV spectra. We show that the majority (~70%) of the main-survey targets are spectroscopically confirmed as quasars, with ~16% galaxies, ~6% stars, and ~8% low-quality spectra lacking reliable features. A non-negligible fraction of the quasars are misidentified by the standard spectroscopic pipeline but we show that the majority can be recovered using post-pipeline "afterburner" quasar-identification approaches. We combine these "afterburners" with our standard pipeline to create a modified pipeline to improve the overall quasar yield. At the depth of the main DESI survey both pipelines achieve a good-redshift purity (reliable redshifts measured within 3000 km/s) of ~99%; however, the modified pipeline recovers ~94% of the visually inspected quasars, as compared to ~86% from the standard pipeline. We demonstrate that both pipelines achieve an median redshift precision and accuracy of ~100 km/s and ~70 km/s, respectively. We constructed composite spectra to investigate why some quasars are missed by the standard spectroscopic pipeline and find that they are more host-galaxy dominated (i.e., distant analogs of "Seyfert galaxies") and/or dust reddened than the standard-pipeline quasars. We also show example spectra to demonstrate the overall diversity of the DESI quasar sample and provide strong-lensing candidates where two targets contribute to a single spectrum.

Peer Review Status:Awaiting Review

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5. ChinaXiv:202303.02635
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The Spectroscopic Data Processing Pipeline for the Dark Energy Spectroscopic Instrument

Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19

J. Guy S. Bailey A. Kremin Shadab Alam D. M. Alexander C. Allende Prieto S. BenZvi A. S. Bolton D. Brooks E. Chaussidon A. P. Cooper K. Dawson A. de la Macorra A. Dey Biprateep Dey G. Dhungana D. J. Eisenstein A. Font-Ribera J. E. Forero-Romero E. Gaztañaga

Abstract： We describe the spectroscopic data processing pipeline of the Dark Energy Spectroscopic Instrument (DESI), which is conducting a redshift survey of about 40 million galaxies and quasars using a purpose-built instrument on the 4-m Mayall Telescope at Kitt Peak National Observatory. The main goal of DESI is to measure with unprecedented precision the expansion history of the Universe with the Baryon Acoustic Oscillation technique and the growth rate of structure with Redshift Space Distortions. Ten spectrographs with three cameras each disperse the light from 5000 fibers onto 30 CCDs, covering the near UV to near infrared (3600 to 9800 Angstrom) with a spectral resolution ranging from 2000 to 5000. The DESI data pipeline generates wavelength- and flux-calibrated spectra of all the targets, along with spectroscopic classifications and redshift measurements. Fully processed data from each night are typically available to the DESI collaboration the following morning. We give details about the pipeline's algorithms, and provide performance results on the stability of the optics, the quality of the sky background subtraction, and the precision and accuracy of the instrumental calibration. This pipeline has been used to process the DESI Survey Validation data set, and has exceeded the project's requirements for redshift performance, with high efficiency and a purity greater than 99 percent for all target classes.

Peer Review Status:Awaiting Review

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6. ChinaXiv:202303.03917
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DAHe white dwarfs from the DESI survey

Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19

Christopher J. Manser Boris T. Gänsicke Keith Inight Akshay Robert S. Ahlen C. Allende Prieto D. Brooks A. P. Cooper A. de la Macorra A. Font-Ribera K. Honscheid T. Kisner M. Landriau Aaron M. Meisner R. Miquel Jundan Nie C. Poppett Gregory Tarlé Zhimin Zhou

Abstract： A new class of white dwarfs, dubbed DAHe, that present Zeeman-split Balmer lines in emission has recently emerged. However, the physical origin of these emission lines remains unclear. We present here a sample of 21 newly identified DAHe systems and determine magnetic field strengths and (for a subset) periods which span the ranges of ~ 6.5 -- 147 MG and ~ 0.4 -- 36 h respectively. All but four of these systems were identified from the Dark Energy Spectroscopic Instrument (DESI) survey sample of more than 47000 white dwarf candidates observed during its first year of observations. We present detailed analysis of the new DAHe WDJ161634.36+541011.51 with a spin period of 95.3 min, which exhibits an anti-correlation between broadband flux and Balmer line strength that is typically observed for this class of systems. All DAHe systems cluster closely on the Gaia Hertzsprung-Russell diagram where they represent ~ 1 per cent of white dwarfs within that region. This grouping further solidifies their unexplained emergence at relatively late cooling times and we discuss this in context of current formation theories. Nine of the new DAHe systems are identifiable from SDSS spectra of white dwarfs that had been previously classified as featureless DC-type systems. We suggest high S/N, unbiased observations of DCs as a possible route for discovering additional DAHe systems.

Peer Review Status:Awaiting Review

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7. ChinaXiv:202303.03337
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The VST ATLAS Quasar Survey I: Catalogue

Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19

Alice Eltvedt T. Shanks N. Metcalfe B. Ansarinejad L. F. Barrientos R. Sharp U. Malik D. N. A. Murphy M. Irwin M. Wilson D. M. Alexander A. Kovacs J. Garcia-Bellido S. Ahlen D. Brooks A. de la Macorra A. Font-Ribera S. Gontcho a Gontcho K. Honscheid A. Meisner

Abstract： We present the VST ATLAS Quasar Survey, consisting of $\sim1,229,000$ quasar (QSO) candidates with $162.2$. One of the aims of this catalogue is to select QSO targets for the 4MOST Cosmology Redshift Survey. To guide our selection, we use X-ray/UV/optical/MIR data in the extended William Herschel Deep Field (WHDF) where we find a $g<22.5$ broad-line QSO density of $269\pm67$ deg$^{-2}$, roughly consistent with the expected $\sim196$ deg$^{-2}$. We also find that $\sim25$% of our QSOs are morphologically classed as optically extended. Overall, we find that in these deep data, MIR, UV and X-ray selections are all $\sim70-90$% complete while X-ray suffers less contamination than MIR and UV. MIR is however more sensitive than X-ray or UV to $z>2.2$ QSOs at $g<22.5$ and the eROSITA limit. We then adjust the selection criteria from our previous 2QDES pilot survey and prioritise VST ATLAS candidates that show both UV and MIR excess, while also selecting candidates initially classified as extended. We test our selections using data from DESI (which will be released in DR1) and 2dF to estimate the efficiency and completeness of our selections, and finally we use ANNz2 to determine photometric redshifts for the QSO candidate catalogue. Applying over the $\sim4700$ deg$^2$ ATLAS area gives us $\sim917,000$ $z<2.2$ QSO candidates of which 472,000 are likely to be $z<2.2$ QSOs, implying a sky density of $\sim$100 deg$^{-2}$, which our WHDF analysis suggests will rise to at least 130 deg$^{-2}$ when eROSITA X-ray candidates are included. At $z>2.2$, we find $\sim310,000$ candidates, of which 169,000 are likely to be QSOs for a sky density of $\sim36$ deg$^{-2}$.

Peer Review Status:Awaiting Review

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8. ChinaXiv:202303.03288
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A framework to measure the properties of intergalactic metal systems with two-point flux statistics

Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19

Naim Göksel Karaçaylı Paul Martini David H. Weinberg Vid Iršič J. Aguilar S. Ahlen D. Brooks A. de la Macorra A. Font-Ribera S. Gontcho A Gontcho J. Guy T. Kisner R. Miquel C. Poppett C. Ravoux M. Schubnell G. Tarlé B. A. Weaver Z. Zhou

Abstract： The abundance, temperature, and clustering of metals in the intergalactic medium are important parameters for understanding their cosmic evolution and quantifying their impact on cosmological analysis with the Ly $\alpha$ forest. The properties of these systems are typically measured from individual quasar spectra redward of the quasar's Ly $\alpha$ emission line, yet that approach may provide biased results due to selection effects. We present an alternative approach to measure these properties in an unbiased manner with the two-point statistics commonly employed to quantify large-scale structure. Our model treats the observed flux of a large sample of quasar spectra as a continuous field and describes the one-dimensional, two-point statistics of this field with three parameters per ion: the abundance (column density distribution), temperature (Doppler parameter) and clustering (cloud-cloud correlation function). We demonstrate this approach on multiple ions (e.g., C IV, Si IV, Mg II) with early data from the Dark Energy Spectroscopic Instrument (DESI) and high-resolution spectra from the literature. Our initial results show some evidence that the C IV abundance is higher than previous measurements and evidence for abundance evolution over time. The first full year of DESI observations will have over an order of magnitude more quasar spectra than this study. In a future paper we will use those data to measure the growth of clustering and its impact on the Ly $\alpha$ forest, as well as test other DESI analysis infrastructure such as the pipeline noise estimates and the resolution matrix.

Peer Review Status:Awaiting Review

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9. ChinaXiv:202303.04059
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Target Selection and Validation of DESI Luminous Red Galaxies

Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19

Rongpu Zhou Biprateep Dey Jeffrey A. Newman Daniel J. Eisenstein K. Dawson S. Bailey A. Berti J. Guy Ting-Wen Lan H. Zou J. Aguilar S. Ahlen Shadab Alam D. Brooks A. de la Macorra A. Dey G. Dhungana K. Fanning A. Font-Ribera S. Gontcho A Gontcho

Abstract： The Dark Energy Spectroscopic Instrument (DESI) is carrying out a 5-year survey that aims to measure the redshifts of tens of millions of galaxies and quasars, including 8 million luminous red galaxies (LRGs) in the redshift range of $0.4展开 -->

Peer Review Status:Awaiting Review

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