Fit J001554.18+560257.5

This example adapts the single-object qsofitmore tutorial to qsospec. The quasar was observed with the Lijiang 2.4 m Telescope and belongs to the sample of Galactic-plane quasars in Fu et al. (2022). Its relatively large \(E(B-V)\) is expected from that Galactic-plane selection.

Prerequisites

Configure the Planck GNILC map as described in Configure Galactic dust maps. Download the example CSV spectrum or run the example from a qsospec source checkout.

Fit and archive the spectrum

The CSV stores observed wavelength in Angstrom and flux density and uncertainty in physical cgs units. These arrays have not been corrected for foreground Galactic extinction.

from pathlib import Path

import pandas as pd
import qsospec

data_path = Path(
    "examples/data/spec_J001554.18+560257.5_LJT.csv"
)
table = pd.read_csv(data_path)

spectrum = qsospec.Spectrum.from_arrays(
    table["lam"],
    table["flux"],
    err=table["err"],
    z=0.1684,
    wave_frame="observed",
    ra=3.97576206,
    dec=56.04931383,
    flux_unit="cgs",
    source=str(data_path),
    galactic_extinction_corrected=False,
)

result = qsospec.fit_object_to_store(
    spectrum,
    "runs/J001554.18+560257.5_auto_host",
    object_id="J001554.18+560257.5",
    global_config=qsospec.GlobalContinuumConfig(
        power_law=qsospec.PowerLawConfig(mode="auto")
    ),
    run_host_decomp=True,
    template_root="~/tools/ppxf_data",
    template_file="spectra_emiles_9.0.npz",
    write_qa=True,
)

fit_object_to_store queries Planck, applies the F99 correction in the observed frame, converts wavelength and flux density to the rest frame, runs pPXF on the corrected rest-frame-normalized spectrum, subtracts the inferred host, selects the single or broken power law, and writes the run and QA plot.

The resulting QA figure shows the corrected total spectrum in the overview. Because host decomposition is enabled, its zoom panels show the host-subtracted spectrum and model. The title reports the applied Planck \(E(B-V)\). Both wavelength and \(F_\lambda\) use the prepared rest-frame convention.

J001554.18+560257.5 fitted with automatic power-law selection and pPXF host decomposition. The overview information box identifies the host-subtracted zoom-panel convention.

Inspect the outputs

dust = result.metadata["galactic_extinction"]
print("E(B-V):", dust["applied_ebv"])
print("Dust map:", dust["source"])
print("QA plot:", result.output_files["main_qa"])
print("Power law:", result.metadata["power_law_mode_selected"])
print("Host enabled:", result.host_decomp_enabled)

for recipe_id, status in result.complex_statuses.items():
    print(recipe_id, status)

for warning in result.warnings:
    print(warning.code, warning.message)

Reload the archived model without refitting:

archived = qsospec.load_model(
    "runs/J001554.18+560257.5_auto_host",
    "J001554.18+560257.5",
)

Already-corrected arrays

If the supplied flux and uncertainty have already been corrected for Milky Way extinction, declare that when constructing the spectrum:

spectrum = qsospec.Spectrum.from_arrays(
    table["lam"],
    table["flux"],
    err=table["err"],
    z=0.1684,
    flux_unit="cgs",
    galactic_extinction_corrected=True,
)

The high-level workflow then preserves the arrays and records declared_corrected provenance.

The Galactic correction and rest-frame conversion always occur before pPXF, in that order. See Fit with host decomposition for alternative host-template configuration.