The spatial distribution of galaxy clusters provides a reliable tracer of the large-scale distribution of matter in the Universe. The clustering signal depends on intrinsic cluster properties and cosmological parameters. The ability of eROSITA onboard Spectrum-Roentgen-Gamma (SRG) to discover galaxy clusters allows probing the association of extended X-ray emission to dark matter haloes. We aim to measure the projected two-point correlation function to study the occupation of dark matter halos by clusters and groups detected by the first eROSITA all-sky survey (eRASS1). We create five volume-limited samples probing clusters with different redshift and X-ray luminosity. We interpret the correlation function with halo occupation distribution (HOD) and halo abundance matching (HAM) models. We simultaneously fit cosmological parameters and halo bias of a flux-limited sample of 6493 clusters with purity > 96%. Results. We obtain a detailed view of the halo occupation for eRASS1 clusters. The fainter population at low redshift (S0: LX = 4.63E43 erg/s, 0.1 < z < 0.2) is the least biased compared to dark matter, with b = 2.95 $\pm$ 0.21. The brightest clusters up to higher redshift (S4: LX = 1.77E44 erg/s , 0.1 < z < 0.6) exhibit a higher bias b = 4.34 $\pm$ 0.62. Satellite groups are rare, with a satellite fraction < 14.9% (8.1) for the S0 (S4) sample. We combine the HOD prediction with a HAM procedure to constrain the scaling relation between LX and mass in a new way and find a scatter of 0.36. We obtain cosmological constraints for the physical cold dark matter density 0.12+0.03-0.02 and an average halo bias b = 3.63+1.02-0.85. We model the clustering of galaxy clusters with a HOD approach for the first time, paving the way for future studies combining eROSITA with 4MOST, SDSS, Euclid, Rubin, and DESI to unravel the cluster distribution in the Universe.
Context. The spatial distribution of galaxy clusters provides a reliable tracer of the large-scale distribution of matter in the Universe. The clustering signal depends on intrinsic cluster properties and cosmological parameters. Aims. The ability of eROSITA on board Spectrum-Roentgen-Gamma (SRG) to discover galaxy clusters allows the association of extended X-ray emission with dark matter haloes to be probed. We measured the projected two-point correlation function to study the occupation of dark matter haloes by clusters and groups detected by the first eROSITA all-sky survey (eRASS1). Methods. We created five volume-limited samples probing clusters with different redshifts and X-ray luminosity values. We interpreted the correlation function with halo occupation distribution (HOD) and halo abundance matching (HAM) models. We simultaneously fit the cosmological parameters and halo bias of a flux-limited sample of 6493 clusters with purity > 96%. Results. We obtained a detailed view of the halo occupation for eRASS1 clusters. The fainter population at low redshift (S0: L̄ X = 4.63 × 10 43 erg s −1 , 0.1 < z < 0.2) is the least biased compared to dark matter, with b = 2.95 ± 0.21. The brightest clusters up to higher redshift (S4: L̄ X = 1.77 × 10 44 erg s −1 , 0.1 < z < 0.6) exhibit a higher bias b = 4.34 ± 0.62. Satellite groups are rare, with a satellite fraction < 14.9% (8.1) for the S0 (S4) sample. We combined the HOD prediction with a HAM procedure to constrain the scaling relation between L X and mass in a new way, and find a scatter of ⟨ σ Lx ⟩ = 0.36. We obtain cosmological constraints for the physical cold dark matter density ω c = 0.12 −0.02 +0.03 and an average halo bias b = 3.63 −0.85 +1.02 . Conclusions. We modelled the clustering of galaxy clusters with a HOD approach for the first time, paving the way for future studies combining eROSITA with 4MOST, SDSS, Euclid , Rubin , and DESI to unravel the cluster distribution in the Universe.
The project uses QuTiP, a quantum computing framework, to simulate interactions between two-qubits coupled with each other via three resonators. The main aim of this project is to build machinery of techniques to understand complex qubit-cavity interactions using QuTiP's functionalities. The system simulated mimics the one constructed by McKay et. al. (M15) and the results of the simulations closely agree with M15's experimental results. The effect of the coupling strength between the qubits and the cavities is studied. It was observed that stronger couplings generated larger separations between the eigen-modes. Studies involving resonance were used to construct the iSWAP gate, a universal quantum logic gate. This study showed the importance of external thermal losses due to cavity dissipation, and qubit decay and dephasing. The Landau-Zener model was tested for the case of multiple crossing; the model motivated the comparison of three scenarios where the 2 qubits were coupled via 1 cavity, 3 cavities, and 6 cavities. The study concluded that having multiple modes, which is a consequence of having multiple cavities, is advantageous for transferring energy from the qubit to the cavity. Finally, the ac-Stark shift was measured in the system and its dynamics showed excellent agreement with the experimental results obtained by M15.
The galaxy population shows a characteristic bimodal distribution based on the star formation activity and is sorted into star-forming or quiescent. These two subpopulations have a tendency to be located in different mass halos. The circumgalactic medium (CGM), as the gas repository for star formation, might contain the answer to the mystery of the formation of such bimodality. Here we consider the bimodality of the galaxy population and study the difference between the properties of the hot CGM around star-forming and quiescent galaxies. We used the X-ray data from the first four SRG/eROSITA all-sky surveys (eRASS:4). We selected central star-forming and quiescent galaxies from the Sloan Digital Sky Survey DR7 with stellar mass $10.0< or halo mass $11.5< 200m /M_ within spectroscopic redshift spec <0.2$, and we built approximately volume-limited galaxy samples. We stacked the X-ray emission around star-forming and quiescent galaxies, respectively. We masked detected point sources and carefully modeled the X-ray emission from unresolved active galaxy nuclei (AGN) and X-ray binaries (XRB) to detect the X-ray emission from the hot CGM. We measured the X-ray surface brightness ($S_ X, CGM $) profiles and integrated the X-ray emission from hot CGM within $R_ 500c $ ($L_ X, CGM $) to provide the scaling relations between $L_ X, CGM $ and galaxies' stellar or halo mass. We detect extended X-ray emission from the hot CGM around star-forming galaxies with $ and quiescent galaxies with $ extending out to 500c $. The $S_ X, CGM $ profile of quiescent galaxies follows a beta model with $ 0.4$, where beta quantifies the slope of the profile. Star-forming galaxies with median stellar masses $ *,med /M_ = 10.7, 11.1, 11.3$ have X, CGM erg/s$, while for quiescent galaxies with $ *,med /M_ X, CGM erg/s$. Notably, quiescent galaxies with $ *,med /M_ > 11.0$ exhibit brighter hot CGM than their star-forming counterparts. In halo mass bins, we detect similar X-ray emission around star-forming and quiescent galaxies with $ 200m /M_ > 12.5$, suggesting that galaxies in the same mass dark matter halos host equally bright hot CGM. We emphasize that the observed X, CGM - M_ 500c $ relations of star-forming and quiescent galaxies are sensitive to the stellar-to-halo mass relation (SHMR). A comparison with cosmological hydrodynamical simulations (EAGLE, TNG100, and SIMBA) reveals varying degrees of agreement, contingent on the simulation and the specific stellar or halo mass ranges considered. Either selected in stellar mass or halo mass, the star-forming galaxies do not host brighter stacked X-ray emission from the hot CGM than their quiescent counterparts at the same mass range. The result provides useful constraints on the extent of feedback's impacts as a mechanism for quenching star formation as implemented in current cosmological simulations.
The eROSITA will deliver an unprecedented volume of X-ray survey observations, 20-30 times more sensitive than ROSAT in the soft band (0.5-2 keV) and for the first time imaging in the hard band (2-10 keV) including galaxy clusters and groups along with obscured and unobscured AGNs. This calls for a powerful theoretical effort to control the systematics and biases that may affect the data analysis. We investigate the detection technique and selection effects in the galaxy group and AGN populations of a mock eROSITA survey at the depth of eRASS:4. We create a $30\times 30$ deg$^{2}$ mock observation based on the cosmological hydrodynamical simulation Magneticum Pathfinder within z=0-0.2. We combine a physical background extracted from the real eFEDS background analysis with realistic simulations of X-ray emission for the hot gas, AGNs and X-ray binaries. We apply a detection procedure equivalent to the reduction done on eRASS data and evaluate the completeness and contamination to reconstruct the luminosity functions of the extended and point sources in the catalogue. We assess the completeness of extended detections as a function of the input X-ray flux and halo. We achieve full recovery of the brightest (most massive) clusters and AGNs. However, a significant fraction of galaxy groups remains undetected. Examining the gas properties between the detected and undetected galaxy groups at fixed halo mass, we observe that the detected population exhibits, on average, higher X-ray brightness compared to the undetected ones. Moreover, we find that X-ray luminosity primarily correlates with the hot gas fraction, rather than temperature or metallicity. Our simulation suggests the presence of a systematic selection effect in current surveys, resulting in X-ray survey catalogues predominantly composed of the lowest-entropy, gas-richest, and highest surface brightness halos on galaxy group scales.
The eROSITA telescope array aboard the Spektrum Roentgen Gamma (SRG) satellite began surveying the sky in December 2019, with the aim of producing all-sky X-ray source lists and sky maps of an unprecedented depth. Here we present catalogues of both point-like and extended sources using the data acquired in the first six months of survey operations (eRASS1; completed June 2020) over the half sky whose proprietary data rights lie with the German eROSITA Consortium. We describe the observation process, the data analysis pipelines, and the characteristics of the X-ray sources. With nearly 930 000 entries detected in the most sensitive 0.2–2.3 keV energy range, the eRASS1 main catalogue presented here increases the number of known X-ray sources in the published literature by more than 60%, and provides a comprehensive inventory of all classes of X-ray celestial objects, covering a wide range of physical processes. A smaller catalogue of 5466 sources detected in the less sensitive but harder 2.3–5 keV band is the result of the first true imaging survey of the entire sky above 2 keV. We present methods to identify and flag potential spurious sources in the catalogues, which we applied for this work, and we tested and validated the astrometric accuracy via cross-comparison with other X-ray and multi-wavelength catalogues. We show that the number counts of X-ray sources in eRASSl are consistent with those derived over narrower fields by past X-ray surveys of a similar depth, and we explore the number counts variation as a function of the location in the sky. Adopting a uniform all-sky flux limit (at 50% completeness) of F 05–2 keV > 5 × 10 −14 erg s −1 cm −2 , we estimate that the eROSITA all-sky survey resolves into individual sources about 20% of the cosmic X-ray background in the 1–2 keV range. The catalogues presented here form part of the first data release (DR1) of the SRG/eROSITA all-sky survey. Beyond the X-ray catalogues, DR1 contains all detected and calibrated event files, source products (light curves and spectra), and all-sky maps. Illustrative examples of these are provided.
Context. The circumgalactic medium (CGM) provides the material needed for galaxy formation and influences galaxy evolution. The hot ( T > 10 6 K ) CGM is poorly detected around galaxies with stellar masses ( M * ) lower than 3 × 10 11 M ⊙ due to the low surface brightness. Aims. We aim to detect the X-ray emission from the hot CGM around Milky Way-mass (MW-mass, log( M * / M ⊙ ) = 10.5 − 11.0) and M31-mass (log( M * / M ⊙ ) = 11.0 − 11.25) galaxies, in addition to measuring the X-ray surface brightness profile of the hot CGM. Methods. We applied a stacking technique to gain enough statistics to detect the hot CGM. We used the X-ray data from the first four SRG/eROSITA All-Sky Surveys (eRASS:4). We discussed how the satellite galaxies could bias the stacking and the method we used to carefully build the central galaxy samples. Based on the SDSS spectroscopic survey and halo-based group finder algorithm, we selected central galaxies with spectroscopic redshifts of z spec < 0.2 and stellar masses of 10.0 < log( M * / M ⊙ ) < 11.5 (85 222 galaxies) – or halo masses of 11.5 < log( M 200m / M ⊙ ) < 14.0 (125,512 galaxies). By stacking the X-ray emission around galaxies, we obtained the mean X-ray surface brightness profiles. We masked the detected X-ray point sources and carefully modeled the X-ray emission from the unresolved active galactic nuclei (AGN) and X-ray binaries (XRB) to obtain the X-ray emission from the hot CGM. Results. We measured the X-ray surface brightness profiles for central galaxies of log( M * / M ⊙ ) > 10.0 or log( M 200m / M ⊙ ) > 11.5. We detected the X-ray emission around MW-mass and more massive central galaxies extending up to the virial radius ( R vir ). The signal-to-noise ratio (S/N) of the extended emission around MW-mass (M31-mass) galaxy is about 3.1 σ (4.7 σ ) within R vir . We used a β model to describe the X-ray surface brightness profile of the hot CGM ( S X, CGM ). We obtained a central surface brightness of log( S X,0 [erg s −1 kpc −2 ]) = 36.7 −0.4 +1.4 (37.1 −0.4 +1.5 ) and β = 0.43 −0.06 +0.10 (0.37 −0.02 +0.04 ) for MW-mass (M31-mass) galaxies. For galaxies with log( M 200m / M ⊙ ) > 12.5, the extended X-ray emission is detected with S/N > 2.8 σ and the S X, CGM can be described by a β model with β ≈ 0.4 and log( S X,0 [erg s −1 kpc −2 ]) > 37.2. We estimated the baryon budget of the hot CGM and obtained a value that is lower than the prediction of ΛCDM cosmology, indicating significant gas depletion in these halos. We extrapolated the hot CGM profile measured within R vir to larger radii and found that within ≈3 R vir , the baryon budget is close to the ΛCDM cosmology prediction. Conclusions. We measured the extended X-ray emission from representative populations of central galaxies around and above MW-mass out to R vir . Our results set a firm footing for the presence of the hot CGM around such galaxies. These measurements constitute a new benchmark for galaxy evolution models and possible implementations of feedback processes therein.
The circumgalactic medium (CGM), as the gas repository for star formation, might contain the answer to the mysterious galaxy quenching and bimodal galaxy population origin. We measured the X-ray emission of the hot CGM around star-forming and quiescent galaxies. We detect extended X-ray emission from the hot CGM around star-forming galaxies with $\log(M_*/M_\odot)>11.0$ and quiescent galaxies with $\log(M_*/M_\odot)>10.5$, extending out to $R_{\rm 500c}$. $L_{\rm X, CGM}$ of star-forming galaxies with median stellar masses $\log(M_{\rm *,med}/M_\odot) = 10.7, 11.1, 11.3$ are approximately $0.8\,, 2.3\,, 4.0 \times 10^{40}\,\rm erg/s$, while for quiescent galaxies with $\log(M_{\rm *,med}/M_\odot) = 10.8, 11.1, 11.4$, they are $1.1\,, 6.2\,, 30 \times 10^{40}\,\rm erg/s$. Notably, quiescent galaxies with $\log(M_{\rm *,med}/M_\odot) > 11.0$ exhibit brighter hot CGM than their star-forming counterparts. In halo mass bins, we detect similar X-ray emission around star-forming and quiescent galaxies with $\log(M_{\rm 200m}/M_\odot) > 12.5$, suggesting that galaxies in the same mass dark matter halos host equally bright hot CGM. We emphasize the observed $L_{\rm X, CGM} - M_{\rm 500c}$ relations of star-forming and quiescent galaxies are sensitive to the stellar-to-halo mass relation (SHMR). A comparison with cosmological hydrodynamical simulations (EAGLE, TNG100, and SIMBA) reveals varying degrees of agreement, contingent on the simulation and the specific stellar or halo mass ranges considered. Either selected in stellar mass or halo mass, the star-forming galaxies do not host brighter stacked X-ray emission from the hot CGM than their quiescent counterparts at the same mass range. The result provides useful constraints on the extent of feedback's impacts as a mechanism for quenching star formation as implemented in current cosmological simulations.
Context. eROSITA will deliver an unprecedented volume of X-ray survey observations, 20 − 30 times more sensitive than ROSAT in the soft band (0.5 − 2.0 keV) and for the first time imaging in the hard band (2 − 10 keV). The final observed catalogue of sources will include galaxy clusters and groups along with obscured and unobscured (active galactic nuclei) AGNs. This calls for a powerful theoretical effort to mitigate potential systematics and biases that may influence the data analysis. Aims. We investigate the detection technique and selection biases in the galaxy group and AGN populations within a simulated X-ray observation conducted at the depth equivalent to a four-year eROSITA survey (eRASS:4). Methods. We generate a mock observation spanning 30 × 30 deg 2 based on the cosmological hydrodynamical simulation Magneticum Pathfinder from z = 0 up to redshift z = 0.2, mirroring the depth of eRASS:4 (with an average exposure of ∼600 s). We combined a physical background from the real eFEDS background analysis with realistic simulations of X-ray emission for the hot gas, AGNs, and XRB. Using a detection method similar to that utilised for eRASS data, we assessed completeness and contamination levels to reconstruct the luminosity functions for both extended and point sources within the catalogue. Results. We define the completeness of extended detections as a function of the input X-ray flux S 500 and halo mass M 500 at the depth of eRASS:4. Notably, we fully recovered the brightest (most massive) galaxy clusters and AGNs. However, a significant fraction of galaxy groups ( M 200 < 10 14 M ⊙ ) remain undetected. Examining gas properties between the detected and undetected galaxy groups at a fixed halo mass, we observe that the detected population typically displays higher X-ray brightness compared to the undetected counterpart. Furthermore, we establish that X-ray luminosity primarily correlates with the hot gas fraction, rather than temperature or metallicity. Our simulation suggests a systematic selection bias in current surveys, leading to X-ray catalogues predominantly composed of the lowest-entropy, gas-richest, and highest surface brightness halos on galaxy group scales.
