arXiv subjects

J. Johansson

Publications and source records attributed to J. Johansson.

At least 55 records · Page 3Linked to original sources

arXiv2017

iPTF16geu: A multiply imaged, gravitationally lensed type Ia supernova

We report the discovery of a multiply-imaged gravitationally lensed Type Ia supernova, iPTF16geu (SN 2016geu), at redshift $z=0.409$. This phenomenon could be identified because the light from the stellar explosion was magnified more than fifty times by the curvature of space around matter in an intervening galaxy. We used high spatial resolution observations to resolve four images of the lensed supernova, approximately 0.3" from the center of the foreground galaxy. The observations probe a physical scale of $\sim$1 kiloparsec, smaller than what is typical in other studies of extragalactic gravitational lensing. The large magnification and symmetric image configuration implies close alignment between the line-of-sight to the supernova and the lens. The relative magnifications of the four images provide evidence for sub-structures in the lensing galaxy.

astro-ph.CO↗

arXiv2017

Spitzer observations of SN 2014J and properties of mid-IR emission in Type Ia supernovae

SN 2014J in M82 is the closest Type Ia supernova (SN Ia) in decades. The proximity allows for detailed studies of supernova physics and provides insights into the circumstellar and interstellar environment. In this work we analyze Spitzer mid-IR data of SN 2014J in the 3.6 and 4.5 μm wavelength range, together with several other nearby and well-studied SNe Ia. We compile the first composite mid-IR light-curve templates from our sample of SNe~Ia, spanning the range from before peak brightness well into the nebular phase. Our observations indicate that SNe Ia form a very homogeneous class of objects at these wavelengths. Using the low-reddening supernovae for comparison, we constrain possible thermal emission from circumstellar dust around the highly reddened SN 2014J. We also study SNe 2006X and 2007le, where the presence of matter in the circumstellar environment has been suggested. No significant mid-IR excess is detected, allowing us to place upper limits on the amount of pre-existing dust in the circumstellar environment. For SN 2014J, $M_{dust} < 10^{-5}$ M$_{\odot}$ within $r_{dust} \sim 10^{17}$ cm, which is insufficient to account for the observed extinction. Similar limits are obtained for SNe 2006X and 2007le.

astro-ph.HE↗

arXiv2016

The Superluminous Transient ASASSN-15lh as a Tidal Disruption Event from a Kerr Black Hole

When a star passes within the tidal radius of a supermassive black hole, it will be torn apart. For a star with the mass of the Sun ($M_\odot$) and a non-spinning black hole with a mass $<10^8 M_\odot$, the tidal radius lies outside the black hole event horizon and the disruption results in a luminous flare. Here we report observations over a period of 10 months of a transient, hitherto interpreted as a superluminous supernova. Our data show that the transient rebrightened substantially in the ultraviolet and that the spectrum went through three different spectroscopic phases without ever becoming nebular. Our observations are more consistent with a tidal disruption event than a superluminous supernova because of the temperature evolution, the presence of highly ionised CNO gas in the line of sight and our improved localisation of the transient in the nucleus of a passive galaxy, where the presence of massive stars is highly unlikely. While the supermassive black hole has a mass $> 10^8 M_\odot$, a star with the same mass as the Sun could be disrupted outside the event horizon if the black hole were spinning rapidly. The rapid spin and high black hole mass can explain the high luminosity of this event.

astro-ph.HE↗

arXiv2016

Early observations of the nearby type Ia supernova SN 2015F

We present photometry and time-series spectroscopy of the nearby type Ia supernova (SN Ia) SN 2015F over $-16$ days to $+80$ days relative to maximum light, obtained as part of the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). SN 2015F is a slightly sub-luminous SN Ia with a decline rate of $Δm15(B)=1.35 \pm 0.03$ mag, placing it in the region between normal and SN 1991bg-like events. Our densely-sampled photometric data place tight constraints on the epoch of first light and form of the early-time light curve. The spectra exhibit photospheric C II $λ6580$ absorption until $-4$ days, and high-velocity Ca II is particularly strong at $<-10$ days at expansion velocities of $\simeq$23000\kms. At early times, our spectral modelling with syn++ shows strong evidence for iron-peak elements (Fe II, Cr II, Ti II, and V II) expanding at velocities $>14000$ km s$^{-1}$, suggesting mixing in the outermost layers of the SN ejecta. Although unusual in SN Ia spectra, including V II in the modelling significantly improves the spectral fits. Intriguingly, we detect an absorption feature at $\sim$6800 Å that persists until maximum light. Our favoured explanation for this line is photospheric Al II, which has never been claimed before in SNe Ia, although detached high-velocity C II material could also be responsible. In both cases the absorbing material seems to be confined to a relatively narrow region in velocity space. The nucleosynthesis of detectable amounts of Al II would argue against a low-metallicity white dwarf progenitor. We also show that this 6800 Å feature is weakly present in other normal SN Ia events, and common in the SN 1991bg-like sub-class.

astro-ph.SR↗

arXiv2016

An Intermediate Type Ia Supernova Between Normal And Super-Chandrasekhar

In this paper, we report observations of a peculiar Type Ia supernova iPTF13asv (a.k.a., SN2013cv) from the onset of the explosion to months after its peak. The early-phase spectra of iPTF13asv show absence of iron absorption, indicating that synthesized iron elements are confined to low-velocity regions of the ejecta, which, in turn, implies a stratified ejecta structure along the line of sight. Our analysis of iPTF13asv's light curves and spectra shows that it is an intermediate case between normal and super-Chandrasekhar events. On the one hand, its light curve shape (B-band $Δm_{15}=1.03\pm0.01$) and overall spectral features resemble those of normal Type Ia supernovae. On the other hand, similar to super-Chandrasekhar events, it shows large peak optical and UV luminosity ($M_B=-19.84\,\rm{mag}$, $M_{uvm2}=-15.5\,\rm{mag}$) a relatively low but almost constant \ion{Si}{2} velocities of about $10,000\,\rm{km}\,\rm{s}^{-1}$, and persistent carbon absorption in the spectra. We estimate a $^{56}$Ni mass of $0.81^{+0.10}_{-0.18}M_\odot$ and a total ejecta mass of $1.59^{+0.45}_{-0.12}M_\odot$. The large ejecta mass of iPTF13asv and its stratified ejecta structure together seemingly favor a double-degenerate origin.

astro-ph.SR↗

arXiv2016

Time-Varying Sodium Absorption in the Type Ia Supernova 2013gh

Temporal variability of narrow absorption lines in high-resolution spectra of Type Ia supernovae (SNe Ia) is studied to search for circumstellar matter. Time series which resolve the profiles of absorption lines such as Na I D or Ca II H&K are expected to reveal variations due to photoionisation and subsequent recombination of the gases. The presence, composition, and geometry of circumstellar matter may hint at the elusive progenitor system of SNe Ia and could also affect the observed reddening law. To date, there are few known cases of time-varying Na I D absorption in SNe Ia, all of which occurred during relatively late phases of the supernova evolution. Photoionisation, however, is predicted to occur during the early phases of SNe Ia, when the supernova peaks in the ultraviolet. We therefore attempt to observe early-time absorption-line variations by obtaining high-resolution spectra of SNe before maximum light. We have obtained photometry and high-resolution spectroscopy of SNe Ia 2013gh and iPTF 13dge, to search for absorption- line variations. Furthermore, we study interstellar absorption features in relation to the observed photometric colours of the SNe. Results. Both SNe display deep Na I D and Ca II H&K absorption features. Furthermore, small but significant variations are detected in a feature of the Na I D profile of SN 2013gh. The variations are consistent with either geometric effects of rapidly moving or patchy gas clouds or photoionisation of Na I gas at R \approx 1019 cm from the explosion. Our analysis indicates that it is necessary to focus on early phases to detect photoionisation effects of gases in the circumstellar medium of SNe Ia. Different absorbers such as Na I and Ca II can be used to probe for matter at different distances from the SNe.

astro-ph.SR↗

arXiv2015

Flash Spectroscopy: Emission Lines from the Ionized Circumstellar Material around $<10$-Day-Old Type II Supernovae

Supernovae (SNe) embedded in dense circumstellar material (CSM) may show prominent emission lines in their early-time spectra ($\leq 10$ days after the explosion), owing to recombination of the CSM ionized by the shock-breakout flash. From such spectra ("flash spectroscopy"), we can measure various physical properties of the CSM, as well as the mass-loss rate of the progenitor during the year prior to its explosion. Searching through the Palomar Transient Factory (PTF and iPTF) SN spectroscopy databases from 2009 through 2014, we found 12 Type II SNe showing flash-ionized (FI) signatures in their first spectra. All are younger than 10 days. These events constitute 14\% of all 84 SNe in our sample having a spectrum within 10 days from explosion, and 18\% of SNe~II observed at ages $<5$ days, thereby setting lower limits on the fraction of FI events. We classified as "blue/featureless" (BF) those events having a first spectrum which is similar to that of a black body, without any emission or absorption signatures. It is possible that some BF events had FI signatures at an earlier phase than observed, or that they lack dense CSM around the progenitor. Within 2 days after explosion, 8 out of 11 SNe in our sample are either BF events or show FI signatures. Interestingly, we found that 19 out of 21 SNe brighter than an absolute magnitude $M_R=-18.2$ belong to the FI or BF groups, and that all FI events peaked above $M_R=-17.6$ mag, significantly brighter than average SNe~II.

astro-ph.HE↗

arXiv2015

Diversity in extinction laws of Type Ia supernovae measured between $0.2$ and $2\,μ\mathrm{m}$

We present ultraviolet (UV) observations of six nearby Type~Ia supernovae (SNe~Ia) obtained with the Hubble Space Telescope, three of which were also observed in the near-IR (NIR) with Wide-Field Camera~3. UV observations with the Swift satellite, as well as ground-based optical and near-infrared data provide complementary information. The combined data-set covers the wavelength range $0.2$--$2~μ$m. By also including archival data of SN 2014J, we analyse a sample spanning observed colour excesses up to $E(B-V)=1.4~$mag. We study the wavelength dependent extinction of each individual SN and find a diversity of reddening laws when characterised by the total-to-selective extinction $R_V$. In particular, we note that for the two SNe with $E(B-V)\gtrsim1~$mag, for which the colour excess is dominated by dust extinction, we find $R_V=1.4\pm0.1$ and $R_V=2.8\pm0.1$. Adding UV photometry reduces the uncertainty of fitted $R_V$ by $\sim50\,$% allowing us to also measure $R_V$ of individual low-extinction objects which point to a similar diversity, currently not accounted for in the analyses when SNe~Ia are used for studying the expansion history of the universe.

astro-ph.HE↗

arXiv2015

First 230 GHz VLBI Fringes on 3C 279 using the APEX Telescope

We report about a 230 GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO). We installed VLBI equipment and measured the APEX station position to 1 cm accuracy (1 sigma). We then observed 3C 279 on 2012 May 7 in a 5 hour 230 GHz VLBI track with baseline lengths of 2800 M$λ$ to 7200 M$λ$ and a finest fringe spacing of 28.6 micro-arcseconds. Fringes were detected on all baselines with SNRs of 12 to 55 in 420 s. The correlated flux density on the longest baseline was ~0.3 Jy/beam, out of a total flux density of 19.8 Jy. Visibility data suggest an emission region <38 uas in size, and at least two components, possibly polarized. We find a lower limit of the brightness temperature of the inner jet region of about 10^10 K. Lastly, we find an upper limit of 20% on the linear polarization fraction at a fringe spacing of ~38 uas. With APEX the angular resolution of 230 GHz VLBI improves to 28.6 uas. This allows one to resolve the last-photon ring around the Galactic Center black hole event horizon, expected to be 40 uas in diameter, and probe radio jet launching at unprecedented resolution, down to a few gravitational radii in galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in detail, follow-up observations with APEX and five other mm-VLBI stations have been conducted (March 2013) and are being analyzed.

astro-ph.IM↗

arXiv2015

Strong Ultraviolet Pulse From a Newborn Type Ia Supernova

Type Ia supernovae are destructive explosions of carbon oxygen white dwarfs. Although they are used empirically to measure cosmological distances, the nature of their progenitors remains mysterious, One of the leading progenitor models, called the single degenerate channel, hypothesizes that a white dwarf accretes matter from a companion star and the resulting increase in its central pressure and temperature ignites thermonuclear explosion. Here we report observations of strong but declining ultraviolet emission from a Type Ia supernova within four days of its explosion. This emission is consistent with theoretical expectations of collision between material ejected by the supernova and a companion star, and therefore provides evidence that some Type Ia supernovae arise from the single degenerate channel.

astro-ph.SR↗

arXiv2015

Supernova spectra below strong circum-stellar interaction

We construct spectra of supernovae interacting strongly with a circumstellar medium (CSM) by adding SN templates, a black-body continuum and an emission-line spectrum. In a Monte Carlo simulation we generate more than 800 spectra, distribute them to 10 different classifiers and study how the different simulation parameters affect the appearance of the spectra. SNe IIn showing some structure over the continuum were characterized as SNe IInS. We demonstrate that the flux ratio of the underlying SN to the continuum fv is the most important parameter determining the spectral classification. Thermonuclear SNe get progressively classified as Ia-CSM, IInS and IIn as fv decreases. The transition between Ia-CSM and IInS occurs at fv~0.2-0.3. It shown that SNe Ia-CSM are found at the magnitude range -19.5> M >-21.6, in good agreement with observations, and that the faintest SN IIn that can hide a SN Ia has M = -20.1. The sample of SNe Ia-CSM shows an association with 91T-like SNe Ia. Our experiment does not support that this association is due to a luminosity bias (91T-like being brighter than normal Ia). We therefore conclude that this association has real physical origins and we propose that 91T-like explosions result from single degenerate progenitors. Despite the similarities between SNe Ibc and SNe Ia, the number of misclassifications between these types was small and mostly at low S/N. Combined with the luminosity function needed to reproduce the observed SN Ia-CSM luminosities, it is unlikely that SNe Ibc constitute an important contaminant within this sample. We show how Type II spectra transition to IIn and how the Ha profiles vary with fv. SNe IIn fainter than M = -17.2 are unable to mask SNe IIP brighter than M = -15. A simulation including radiative transfer shows that our simplified model is a good first order approximation. The spectra obtained are in good agreement with real data.

astro-ph.SR↗

arXiv2015

Strong near-infrared carbon in the Type Ia supernova iPTF13ebh

We present near-infrared (NIR) time-series spectroscopy, as well as complementary ultraviolet (UV), optical, and NIR data, of the Type Ia supernova (SN Ia) iPTF13ebh, which was discovered within two days from the estimated time of explosion. The first NIR spectrum was taken merely 2.3 days after explosion and may be the earliest NIR spectrum yet obtained of a SN Ia. The most striking features in the spectrum are several NIR C I lines, and the C I λ1.0693 μm line is the strongest ever observed in a SN Ia. Interestingly, no strong optical C II counterparts were found, even though the optical spectroscopic time series began early and is densely-cadenced. Except at the very early epochs, within a few days from the time of explosion, we show that the strong NIR C I compared to the weaker optical C II appears to be general in SNe Ia. iPTF13ebh is a fast decliner with Δm15(B) = 1.79 $\pm$ 0.01, and its absolute magnitude obeys the linear part of the width-luminosity relation. It is therefore categorized as a "transitional" event, on the fast-declining end of normal SNe Ia as opposed to subluminous/91bg-like objects. iPTF13ebh shows NIR spectroscopic properties that are distinct from both the normal and subluminous/91bg-like classes, bridging the observed characteristics of the two classes. These NIR observations suggest composition and density of the inner core similar to that of 91bg-like events, and a deep reaching carbon burning layer not observed in slower declining SNe Ia. There is also a substantial difference between the explosion times inferred from the early-time light curve and the velocity evolution of the Si II λ0.6355 μm line, implying a long dark phase of ~ 4 days.

astro-ph.SR↗

arXiv2015

No trace of a single-degenerate companion in late spectra of SNe 2011fe and 2014J

Left-over, ablated material from a possible non-degenerate companion can reveal itself after about one year in spectra of Type Ia SNe (SNe Ia). We have searched for such material in spectra of SN 2011fe (at 294 days after the explosion) and for SN 2014J (315 days past explosion). The observations are compared with numerical models simulating the expected line emission. The spectral lines sought for are H-alpha, [O I] 6300 and [Ca II] 7291,7324, and the expected width of these lines is about 1000 km/s. No signs of these lines can be traced in any of the two supernovae. When systematic uncertainties are included, the limits on hydrogen-rich ablated gas in SNe 2011fe and 2014J are 0.003 M_sun and 0.0085 M_sun, respectively, where the limit for SN 2014J is the second lowest ever, and the limit for SN 2011fe is a revision of a previous limit. Limits are also put on helium-rich ablated gas. These limits are used, in conjunction with other data, to argue that these supernovae can stem from double-degenerate systems, or from single-degenerate systems with a spun up/spun down super-Chandrasekhar white dwarf. For SN 2011fe, other types of hydrogen-rich donors can likely be ruled out, whereas for SN 2014J a main-sequence donor system with large intrinsic separation is still possible. Helium-rich donor systems cannot be ruled out for any of the two supernovae, but the expected short delay time for such progenitors makes this possibility less likely, especially for SN 2011fe. The broad [Ni II] 7378 emission in SN 2014J is redshifted by about +1300 km/s, as opposed to the known blueshift of roughly -1100 km/s for SN 2011fe. [Fe II] 7155 is also redshifted in SN 2014J. SN 2014J belongs to a minority of SNe Ia that both have a nebular redshift of [Fe II] 7155 and [Ni II] 7378, and a slow decline of the Si II 6355 absorption trough just after B-band maximum.

astro-ph.HE↗

arXiv2014

The peculiar extinction law of SN2014J measured with The Hubble Space Telescope

The wavelength-dependence of the extinction of Type Ia SN2014J in the nearby galaxy M82 has been measured using UV to near-IR photometry obtained with the Hubble Space Telescope, the Nordic Optical Telescope, and the Mount Abu Infrared Telescope. This is the first time that the reddening of a SN Ia is characterized over the full wavelength range of $0.2$-$2$ microns. A total-to-selective extinction, $R_V\geq3.1$, is ruled out with high significance. The best fit at maximum using a Galactic type extinction law yields $R_V = 1.4\pm0.1$. The observed reddening of SN2014J is also compatible with a power-law extinction, $A_λ/A_V = \left( λ/ {λ_V} \right)^{p}$ as expected from multiple scattering of light, with $p=-2.1\pm0.1$. After correction for differences in reddening, SN2014J appears to be very similar to SN2011fe over the 14 broad-band filter light curves used in our study.

astro-ph.HE↗

arXiv2014

Early Observations and Analysis of the Type Ia SN 2014J in M82

We present optical and near infrared (NIR) observations of the nearby Type Ia SN 2014J. Seventeen optical and twenty-three NIR spectra were obtained from 10 days before ($-$10d) to 10 days after (+10d) the time of maximum $B$-band brightness. The relative strengths of absorption features and their patterns of development can be compared at one day intervals throughout most of this period. Carbon is not detected in the optical spectra, but we identify CI $λ$ 1.0693 in the NIR spectra. We find that MgII lines with high oscillator strengths have higher initial velocities than other MgII lines. We show that the velocity differences can be explained by differences in optical depths due to oscillator strengths. The spectra of SN 2014J show it is a normal SN Ia, but many parameters are near the boundaries between normal and high-velocity subclasses. The velocities for OI, MgII, SiII, SII, CaII and FeII suggest that SN 2014J has a layered structure with little or no mixing. That result is consistent with the delayed detonation explosion models. We also report photometric observations, obtained from $-$10d to +29d, in the $UBVRIJH$ and $K_s$ bands. SN 2014J is about 3 magnitudes fainter than a normal SN Ia at the distance of M82, which we attribute to extinction in the host. The template fitting package SNooPy is used to interpret the light curves and to derive photometric parameters. Using $R_V$ = 1.46, which is consistent with previous studies, SNooPy finds that $A_V = 1.80$ for $E(B-V)_{host}=1.23 \pm 0.01$ mag. The maximum $B$-band brightness of $-19.19 \pm 0.10$ mag was reached on February 1.74 UT $ \pm 0.13$ days and the supernova had a decline parameter of $Δm_{15}=1.11 \pm 0.02$ mag.

astro-ph.GA↗

arXiv2014

The rise of SN2014J in the nearby galaxy M82

We report on the discovery of SN2014J in the nearby galaxy M82. Given its proximity, it offers the best opportunity to date to study a thermonuclear supernova over a wide range of the electromagnetic spectrum. The first set of optical, near-IR and mid-IR observations of SN2014J, orchestrated by the intermediate Palomar Transient Factory (iPTF), show that SN2014J is a spectroscopically normal Type Ia supernova, albeit exhibiting high-velocity features in its spectrum and heavily reddened by dust in the host galaxy. Our earliest detections start just hours after the fitted time of explosion. We use high-resolution optical spectroscopy to analyze the dense intervening material and do not detect any evolution in the resolved absorption features during the lightcurve rise. Similarly to other highly reddened Type Ia supernovae, a low value of total-to-selective extinction, Rv < 2, provides the best match to our observations. We also study pre-explosion optical and near-IR images from HST with special emphasis on the sources nearest to the SN location.

astro-ph.GA↗

arXiv2013

Galaxy And Mass Assembly (GAMA): Spectroscopic analysis

The Galaxy And Mass Assembly (GAMA) survey is a multiwavelength photometric and spectroscopic survey, using the AAOmega spectrograph on the Anglo-Australian Telescope to obtain spectra for up to ~300000 galaxies over 280 square degrees, to a limiting magnitude of r_pet < 19.8 mag. The target galaxies are distributed over 0<z<0.5 with a median redshift of z~0.2, although the redshift distribution includes a small number of systems, primarily quasars, at higher redshifts, up to and beyond z=1. The redshift accuracy ranges from sigma_v~50km/s to sigma_v~100km/s depending on the signal-to-noise of the spectrum. Here we describe the GAMA spectroscopic reduction and analysis pipeline. We present the steps involved in taking the raw two-dimensional spectroscopic images through to flux-calibrated one-dimensional spectra. The resulting GAMA spectra cover an observed wavelength range of 3750<lambda<8850 A at a resolution of R~1300. The final flux calibration is typically accurate to 10-20%, although the reliability is worse at the extreme wavelength ends, and poorer in the blue than the red. We present details of the measurement of emission and absorption features in the GAMA spectra. These measurements are characterised through a variety of quality control analyses detailing the robustness and reliability of the measurements. We illustrate the quality of the measurements with a brief exploration of elementary emission line properties of the galaxies in the GAMA sample. We demonstrate the luminosity dependence of the Balmer decrement, consistent with previously published results, and explore further how Balmer decrement varies with galaxy mass and redshift. We also investigate the mass and redshift dependencies of the [NII]/Halpha vs [OIII]/Hbeta spectral diagnostic diagram, commonly used to discriminate between star forming and nuclear activity in galaxies.

astro-ph.CO↗

arXiv2013

Stellar velocity dispersions and emission line properties of SDSS-III/BOSS galaxies

We perform a spectroscopic analysis of 492,450 galaxy spectra from the first two years of observations of the Sloan Digital Sky Survey-III/Baryonic Oscillation Spectroscopic Survey (BOSS) collaboration. This data set has been released in the ninth SDSS data release, the first public data release of BOSS spectra. We show that the typical signal-to-noise ratio of BOSS spectra is sufficient to measure stellar velocity dispersion and emission line fluxes for individual objects. The typical velocity dispersion of a BOSS galaxy is 240 km/s, with an accuracy of better than 30 per cent for 93 per cent of BOSS galaxies. The distribution in velocity dispersion is redshift independent between redshifts 0.15 and 0.7, which reflects the survey design targeting massive galaxies with an approximately uniform mass distribution in this redshift interval. The majority of BOSS galaxies lack detectable emission lines. We analyse the emission line properties and present diagnostic diagrams using the emission lines [OII], Hbeta, [OIII], Halpha, and [NII] (detected in about 4 per cent of the galaxies). We show that the emission line properties are strongly redshift dependent and that there is a clear correlation between observed frame colours and emission line properties. Within in the low-z sample around 0.15<z<0.3, half of the emission-line galaxies have LINER-like emission line ratios, followed by Seyfert-AGN dominated spectra, and only a small fraction of a few per cent are purely star forming galaxies. AGN and LINER-like objects, instead, are less prevalent in the high-z sample around 0.4<z<0.7, where more than half of the emission line objects are star forming. This is a pure selection effect caused by the non-detection of weak Hbeta emission lines in the BOSS spectra. Finally, we show that star forming, AGN and emission line free galaxies are well separated in the g-r vs r-i target selection diagram.

astro-ph.CO↗