About

Michael Strauss is interested in all aspects of extragalactic astronomy and observational cosmology, especially in the context of wide-field imaging and spectroscopic surveys of the sky. He has used large surveys including IRAS and the Sloan Digital Sky Survey to study the large-scale distribution of galaxies to constrain cosmological parameters, the relationship between galaxy properties and their environment, and the nature and evolution of active galactic nuclei (AGN) and quasars at large redshifts. Currently, he is utilizing data from the Hyper Suprime-Cam on the Subaru Telescope to search for distant quasars and to study the properties of the galaxies in which they reside. He is involved in planning for the next generation of large surveys, including the Prime Focus Spectrograph on Subaru and the Rubin Observatory Legacy Survey of Space and Time.

Research topics

• Physics
• Astronomy
• Computer Science
• Astrophysics
• Statistics
• Systems engineering
• Engineering
• Geography
• Astrobiology

Selected publications

• Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs)

  Astronomy and Astrophysics · 2026-01-08

  articleOpen access

  We report on Chandra X-ray observations of four narrow-line quasar candidates at z ∼ 6, selected from the Subaru high-z exploration of low-luminosity quasars (SHELLQs) project, based on the Subaru Hyper Suprime-Cam survey. These objects are characterised by narrow (FWHM ≤ 310 km s −1 ), luminous (> 10 44 erg s −1 ) Ly α , and faint UV continuum ( M 1450 = −22 to −21), prompting us to examine whether they are obscured luminous active galactic nuclei (AGNs) at the epoch of reionization. However, none of these objects were detected by Chandra, giving an upper limit to their rest-frame 2−10 keV luminosity ( L X ) of 2 × 10 44 erg s −1 (2 σ ), assuming a spectral slope of Γ = 2. Subsequent rest-frame optical spectroscopy of these objects by the James Webb Space Telescope, presented in a companion paper, shows weak broad Balmer emission at the base of narrow cores. With the scaling relation for low-redshift AGNs, the observed strong [O III ] λ 5007 flux of these sources would predict L X to be around 10 45 erg s −1 , which is well above the Chandra upper limits. These optical spectra and X-ray quietness are reminiscent of JWST-selected broad-line AGNs. We attribute the weak broad Balmer emission to the broad-line regions hidden partially by optically thick obscuring matter that also hides the optical and X-ray continuum emission from the accretion disc. Compton-thick obscuration, which would strongly suppress X-ray emission, could be due to a dense interstellar medium that is often present in galaxies at high redshifts. Alternatively, the same effect could be obtained from an inflated disc at the innermost radii in a supercritical accretion flow, when the disc is viewed at inclined angles.

  PublisherDOI

• Selecting Clusters and Protoclusters via Stellar Mass Density. II. Application to HSC-SSP Observations

  The Astrophysical Journal · 2025-10-06 · 1 citations

  articleOpen access

  Abstract We present a selection of candidates of clusters and protoclusters of galaxies identified in the photometric data of the HSC-SSP Wide Public Data Release 3 (PDR3), spanning the redshift range 0.1 ≤ z ≤ 2. The selection method, detailed in Vicentin et al., involves detecting massive galaxies located in high-density regions of matter, identified as potential central dominant galaxies, i.e., (proto)brightest cluster galaxies (protoBCGs or BCGs). Probabilistic criteria based on proximity to the candidate central galaxy and the expected stellar mass of member galaxies are applied to identify likely members of each structure. We produced updated photometric redshift estimates using deep learning methods trained on a data set combining spectroscopic redshifts from the HSC-SSP Wide PDR3, high-accuracy photometric redshifts from the COSMOS2020 catalog, and midinfrared data from the unWISE catalog for matched sources. Our method achieves a predicted purity of ∼90% in detecting (proto)clusters, with ≳65% correctly identifying the (proto)BCG. A total of 16,007 candidate (proto)clusters were identified over an effective area of ∼850 deg 2 within the HSC-SSP Wide footprint. Comparisons with other existing catalogs reveal a good level of consistency, while also highlighting that different methods yield complementary discoveries. We further compare richness and halo masses from our optical catalog with those from recent X-ray cluster catalogs (eROSITA and MCXC-II), finding a moderate positive correlation and a scatter of ∼0.4 dex. This catalog provides a valuable new set of targets for the Prime Focus Spectrograph instrument.

  PublisherDOI

• Unveiling the Origin of Fast Radio Bursts by Modeling the Stellar Mass and Star Formation Distributions of Their Host Galaxies

  The Astrophysical Journal · 2025-09-17 · 5 citations

  articleOpen access

  Abstract Diverse formation channels have been proposed to explain the emergence of fast radio bursts (FRBs), yet their origin remains elusive. With improved localization precision, roughly 90 FRBs are now associated with host galaxies. Spectral energy distribution fitting to the host galaxy photometry reveals their stellar masses ( M ⋆ ) and star formation rates (SFRs), enabling discrimination between various formation channels. We conduct an extensive comparison of the stellar mass, SFR, and redshift distributions of 51 FRB hosts and mock generated galaxy samples to test whether FRBs trace SFR or M ⋆ . We incorporate a mass-to-light ratio ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> </mml:mrow> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">r</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">obs</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) prescription to address optical selection biases. In line with K. Sharma et al., we provide evidence in favor of FRB progenitors tracking SFR rather than stellar mass. We show that the shape of the assumed <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> </mml:mrow> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">o</mml:mi> <mml:mi mathvariant="normal">b</mml:mi> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> </mml:msub> </mml:math> distribution affects the predictions, bringing the low-mass end of the stellar mass distribution closer to the data when accounting for the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>SFR</mml:mi> <mml:mo>–</mml:mo> <mml:msub> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msub> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>L</mml:mi> <mml:mi>r</mml:mi> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mi>obs</mml:mi> </mml:msub> </mml:math> correlation. The K -correction effect in the r band is minimal for galaxies at z ≲ 0.7. In the model in which FRBs trace SFR, up to ∼6% of a flux-limited FRB host sample can reside below the star-forming main sequence. Finally, we examine a hybrid model in which a fraction of FRBs tracks stellar mass rather than SFR. This fraction can be as large as ∼40%−50%, suggesting that multiple formation channels are still consistent with observations. The toolkit developed in this work, GALFRB ( https://github.com/loudasnick/GALFRB ; N. Loudas et al.), is publicly available, offering a straightforward way to generate mock galaxy samples suitable for direct comparisons with future FRB host galaxy data.

  PublisherOA PDFDOI

• The Discovery of Little Red Dots in the Local Universe: Signatures of Cool Gas Envelopes

  ArXiv.org · 2025-07-14 · 4 citations

  preprintOpen access

  JWST observations have revealed a population of high-redshift "little red dots" (LRDs) that challenge conventional AGN models. We report the discovery of three local LRDs at $z = 0.1$-$0.2$, initially selected from the SDSS database, with follow-up optical/near-IR spectroscopy and photometry. They exhibit properties fully consistent with those of high-redshift LRDs, including broad hydrogen and helium emission lines, compact morphologies, V-shaped UV-optical SED, declining near-IR continua, and no significant variability. Two sources were targeted but not detected in X-rays with statistical significance. All three sources show blue-shifted He I absorption, while two exhibit H$α$ and Na D absorption lines. We detect full Balmer and Paschen line series in all three objects, along with abundant narrow [Fe II] emission in two. The emission line analyses suggest narrow lines originate from AGN-powered, metal-poor regions with minimal dust; broad lines come from inner regions with exceptionally high density or atypical dust properties; and [Fe II] emission arises from dense gas between broad and narrow-line regions. One of our objects, J1025+1402 (nicknamed $The~Egg$), shows extremely high equivalent width Na D, K I, and Ca II triplet absorption lines, along with other potential low-ionization absorption features, suggesting the presence of a cool ($\sim$5000 K), metal-enriched gas envelope. The optical/near-IR continua of these LRDs are also consistent with theoretical models featuring an atmosphere around black holes. The WISE-detected IR emission is consistent with weak dust emission of $T \sim 10^2-10^3$ K. We propose a conceptual model consisting of a largely thermalized cool-gas envelope surrounding the central black hole and an extended emission line region with high-density outflowing gas to explain the observed properties of these local LRDs.

  PublisherOA PDFDOI

• Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). XXIV. 54 New Quasars and Candidate Obscured Quasars at $5.71 \le z \le 7.02$

  ArXiv.org · 2025-08-28

  preprintOpen access

  We present spectroscopic identification of 43 quasars and 11 candidate obscured quasars in the epoch of reionization (EoR) at $5.71 \le z \le 7.02$, along with 29 galaxies at similar redshifts. This is the 24th publication from the Subaru High-$z$ Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) imaging survey to search for EoR quasars. The HSC-SSP survey has completed, and this paper is likely the final installment of major (unobscured) quasar discoveries from the SHELLQs project. In addition to the EoR objects, we identified five strong [O III] line emitters at $z &lt; 1$, 30 Galactic brown dwarfs, and 14 passive galaxies at $z \sim 2$, which contaminated our sample of photometric quasar candidates. The present paper focuses on describing the immediate outcome of the spectroscopic observations, while a statistical analysis of the full SHELLQs sample will be presented in our next publication.

  PublisherOA PDFDOI

• ECONOMIC EVALUATION AND DIAGNOSTIC ACCURACY OF COMPUTERIZED DETECTION ON LUNG RADIOGRAPHS IN CORONAVIRUS INFECTION (COVID-19) COMPLICATED BY PNEUMONIA

  Vestnik of the Kyrgyz-Russian Slavic University · 2025-01-01

  article

  To strengthen COVID-19 containment strategies, an addition to the polymerase chain reaction, recognized as the gold standard for diagnosis, but limited by high cost and complex operation, is needed. Chest X-ray is widely used for screening due to its accessibility, but interpretation difficulties due to weak radiological features limit its accuracy. Artificial intelligence offers a solution for automated, accurate and fast X-ray analysis. The economic and diagnostic aspects of using artificial intelligence to detect pneumonia in COVID-19 are being evaluated. The study was conducted in X-ray rooms using specially designed X-ray description templates. The study compared the accuracy of the diagnosis of pneumonia in COVID-19 among three radiologists and artificial intelligence: doctors showed an accuracy of 92-94%, artificial intelligence – 91%. Artificial intelligence accelerates the process by analyzing the image in 7-12 seconds, whereas doctors' time ranged from 302 to 840 seconds (median 452 seconds). A survey of patients showed that 42% support the use of artificial intelligence, 30% disagree, and 28% found it difficult to answer. In a study with 167 participants, the use of artificial intelligence reduced diagnostic costs from 48,096 to 11,506 soms, providing savings of 36,589 soms. The technology improves diagnostic accuracy, reduces staff workload, and improves access to medical care. The successful implementation of artificial intelligence requires trained specialists, affordable equipment, information campaigns, and building trust among patients and medical organizations.

  PublisherDOI

• No Galaxy-scale [C ii] Fast Outflow in the z = 6.72 Red Quasar HSC J1205–0000

  The Astrophysical Journal · 2025-02-07 · 3 citations

  articleOpen access

  Abstract HSC 120505.09-000027.9 (J1205–0000) is one of the highest redshift ( z = 6.72) dust-reddened quasars (red quasars) known to date. We present an improved analysis of Atacama Large Millimeter/submillimeter Array data of the [C ii ] 158 μ m line and the underlying rest-frame far-infrared (FIR) continuum emission, previously reported in T. Izumi et al. (2021b), toward J1205–0000. Red quasars are thought to be a transitional phase from an obscured starburst to a luminous blue quasar, in some cases associated with massive outflows driven by the active galactic nucleus (AGN). J1205–0000 has a high FIR luminosity, L FIR = 2.5 × 10 12 L ⊙ and a total IR luminosity of L TIR = 3.5 × 10 12 L ⊙ , corresponding to a star formation rate of ∼528 M ⊙ yr −1 . With the [C ii ]-based dynamical mass of ∼1 × 10 11 M ⊙ , we conclude that J1205–0000 is hosted by a starburst galaxy. In contradiction to T. Izumi et al., our improved analysis shows no hint of a broad component in the [C ii ] line spectrum. Thus there is no evidence for a host galaxy-scale fast [C ii ] outflow, despite the fact that J1205–0000 has fast nuclear ionized outflows seen in the rest-frame UV. We explore several scenarios for this discrepancy (e.g., the early phase of AGN feedback, reliability of the [C ii ] line as a tracer of outflows), and we claim that it is still too early to conclude that there is no significant negative AGN feedback on star formation in this red quasar.

  PublisherDOI

• Cross-correlation of Luminous Red Galaxies with ML-selected AGN in HSC-SSP III: HOD Parameters for Type I and Type II Quasars

  ArXiv.org · 2025-10-13

  preprintOpen access

  Understanding the dark matter (DM) halo environment in which galaxies that host active galactic nuclei (AGN) reside is a window into the nature of supermassive black hole (SMBH) accretion. We apply halo occupation distribution (HOD) modeling tools to interpret the angular cross-correlation functions between $1.5\times10^6$ luminous red galaxies (LRGs) and our $\sim28,500$ Hyper Suprime-Cam + Wide-field Infrared Survey Explorer-selected (and $L_{6 μm}$-limited) AGN to infer the halo properties of distinct quasar samples at physical scales $s&gt;0.1\,{\rm Mpc}$, for $z\in0.7-1.0$. We find that Type I (unobscured) and Type II (obscured) AGN cluster differently, both on small and large physical scales. The derived HODs imply that Type I AGN reside, on average, in substantially ($\sim3\times$) more massive halos ($M_h \sim 10^{13.4} M_\odot$) than Type II AGN ($M_h \sim 10^{12.9} M_\odot$) at $&gt;5σ$ significance. While Type II AGN show one-halo correlations similar to that of galaxies of their average halo mass, the Type I AGN intra-halo clustering signal is significantly shallower. We interpret this observation with HOD methods and find Type I AGN are significantly less likely ($f_{sat}\sim0.05^{+1}_{-0.05}\%$) to be found in satellite galaxies than Type II AGN. We find reddened + obscured AGN to have typical satellite fractions for their inferred average halo mass ($\sim10^{13} M_\odot$), with $f_{sat} \sim 20^{+10}_{-5}\%$. Taken together, these results pose a significant challenge to the strict unified AGN morphological model, and instead suggest that a quasar's spectral class is strongly correlated with its host galaxy's dark matter halo environment. These intriguing results have provided a more complex picture of the SMBH -- DM halo connection, and motivate future analyses of the intrinsic galaxy and accretion properties of AGN.

  PublisherOA PDFDOI

• Subaru High-<i>z</i> Exploration of Low-luminosity Quasars (SHELLQs). XXIV. 54 New Quasars and Candidate Obscured Quasars at 5.71 ≤ <i>z</i> ≤ 7.02

  The Astrophysical Journal Supplement Series · 2025-10-01 · 4 citations

  articleOpen access

  Abstract We present spectroscopic identification of 43 quasars and 11 candidate obscured quasars in the epoch of reionization (EoR) at 5.71 ≤ z ≤ 7.02, along with 29 galaxies at similar redshifts. This is the 24th publication from the Subaru High- z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) imaging survey to search for EoR quasars. The HSC-SSP survey has finished, and this paper is likely the final installment of major (unobscured) quasar discoveries from the SHELLQs project. In addition to the EoR objects, we identified five strong [O iii ] line emitters at z &lt; 1, 30 Galactic brown dwarfs, and 14 passive galaxies at z ∼ 2, which contaminated our sample of photometric quasar candidates. The present paper focuses on describing the immediate outcome of the spectroscopic observations, while a statistical analysis of the full SHELLQs sample will be presented in our next publication.

  PublisherDOI

• A post-starburst pathway for the formation of massive galaxies and black holes at z &gt; 6

  Nature Astronomy · 2025-08-11 · 15 citations

  articleOpen access
  PublisherOA PDFDOI

Recent grants

• The Clustering of High Redshift Quasars on Large and Small Scales

  NSF · $403k · 2007–2013

• A Complete Census of Seyferts and Obscured AGN from the Sloan Digital Sky Survey

  NSF · $326k · 2003–2007

Frequent coauthors

• Donald P. Schneider

  272 shared

• Xiaohui Fan

  257 shared

• Gordon T. Richards

  240 shared

• Donald G. York

  192 shared

• James E. Gunn

  178 shared

• David J. Schlegel

  169 shared

• Robert H. Lupton

  167 shared

• Patrick B. Hall

  161 shared

Labs

• Michael Strauss | Department of Astrophysical SciencesPI

Education

• BA, PhD, Physics, Astronomy

  University of California Berkeley

  1989